Trombe duvarlı pasif sistemlerde hava kanalının sayısal incelenmesi
Numerical simulation of trombe wall channel
- Tez No: 66724
- Danışmanlar: PROF. DR. NİLÜFER EĞRİCAN
- Tez Türü: Yüksek Lisans
- Konular: Makine Mühendisliği, Mechanical Engineering
- Anahtar Kelimeler: Belirtilmemiş.
- Yıl: 1997
- Dil: Türkçe
- Üniversite: İstanbul Teknik Üniversitesi
- Enstitü: Fen Bilimleri Enstitüsü
- Ana Bilim Dalı: Enerji Ana Bilim Dalı
- Bilim Dalı: Belirtilmemiş.
- Sayfa Sayısı: 81
Özet
ÖZET Bina dizaynında göz önüne alınan özelliklerin başında binanın bulunduğu yerin iklimsel karakterinden maksimum oranda yarar sağlamak gelir, iklimsel özelliklerden en önemlisi olan güneş ışınımı vasıtasıyla ısıl konforu düşük enerji tüketimi ile sağlama güneş evi dizaynındaki temel amaçtır. Güneş evleri aktif ve pasif ısıtma sistemi olarak ikiye ayrılırlar. Pasif sistemlerde aktif sistemlerde olduğu gibi toplanan enerjiyi ısıtılacak mekana transfer eden bir çalışma sıvısı ve enerji transfer mekanizmasına ihtiyaç yoktur. Aktif sistemin tüm fonksiyonları yapı elemanları vasıtasıyla gerçekleştirilir. Bu çalışmada, pasif sistem türleri içerisinde yer alan Trombe Duvarlı sistem ele alınmıştır. Trombe Duvarı hava kanalı güneş enerjisini en etkin biçimde kullanacak dizaynın belirlenmesinde can alıcı kısmı oluşturduğundan hava kanalı üzerinde yoğunlaşılmıştır. Kenar oranı sabit tutularak laminer akış bölgesinde sonlu farklar yöntemi kullanılarak hazırlanan bilgisayar programı ile sayısal çözüm yapılmış, programın sınır şartlarını oluşturan veriler, güneş enerjisi sistemlerini tek boyutlu olarak çözümleyen TRNSYS paket programından elde edilmiştir. İnceleme sabit ventilasyon deliği konumunda dört farklı Grashof sayısı alınarak, sabit Grashof sayısında ventilasyon deliklerinin yeri değiştirilerek, sabit Grashof sayısı ve ventilasyon deliği konumunda giriş hızı için pratikte karşılaşılabilecek maksimum ve minumum değerler alınarak yapılmıştır. Her durumdaki akış profilleri karşılaştırılmış, eş hız ve eş sıcaklık eğrilerinden de yararlanılarak sonuçlar irdelenmiştir. XII
Özet (Çeviri)
SUMMARY NUMERICAL SIMULATION OF TROMBE WALL CHANNEL The different kinds of building construction which were utilized solar energy and supplied thermal comfort had been considered even from the ancient times. For example, the buildings were shaped and the different part of the building located and oriented to take maximum advantage of the climate. Especially, south faced window was widely used to absorb as much of the winter sun as possible. There are two approaches to low energy house design. The first, which is known as an active system uses solar collected panels, storage tanks or bins, an energy transfer mechanism and an energy distribution system. The active system always employs one or more working fluids which collects, transfers, stores and distributes the collected solar energy. The working fluids are circulated by means of fans or pumps. The second approach, passive design seeks to reduce the house's energy budget by close attention to orientation, insulation, window placement and design, and to the subtleties of the energy transfer properties of building materials. Since solar gains are presented in every building, all buildings are passively solar-heated to some extend. It is termed a solar building when the building has been designed to optimize the use of solar energy and when solar energy contributes substantially to the heating requirements of the building. Conceptual comparison of passive and active designs are made by considering the passively designed house as acting as absorber, store and delivery-there is usually no working fluid: all functions of the active systems are carried out by the building materials themselves. Conscious scientific application of solar energy for passive heating may be said to have started in 1881 when Professor E.L. Morse was granted a patent on a glazed south facing dark wall for keeping the house warm. This idea was applied by Professor Morse only to one room of his house and not followed up by either him or others for a very long time. Morse's concept was repented by Trombe (1972,1974) who, starting in 1972 built a series of houses at Odeillo in France and made an engineering success of the idea. Hollinsworth had also employed such a wall in an experimental house. In 1952 the Kech brothers designed a 24 unit solar home development in which they used double-glazing to maintain comfortable conditions despite the biting cold of northern Illinois winters. Overheating and wide temperature swings were problems encountered in these and similar designs; openable windows or ventilating fans were generally required to maintain comfort in winter. Hay and Yellot (1969) introduced the concept of a roof pond to store heat during the days and deliver it to the living space in the night in winter. The same system could be employed in hot weather to cool the building. Moveable insulation is a special feature of the system. With the advent of the energy crisis there was a renewed interest in xmthose aspects of architecture which contributed to thermal comfort in a building without (or with rninimum) expenditure of energy. This led to the formal recognition of the passive (or natural) heating and cooling of buildings as a distinct science. There are three key physical processes that make passive solar heating possible: solar gain, heat storage, and heat distribution. The building works well or poorly, depending primarily on how it is designed; that is, the design that determines whether the natural processes will conform to the needs of the building at any particular time. Solar gains are controlled primarily by the location, orientation, and shading of the windows in the buildings. Heat storage is in the normal materials of the building, and distribution is by radiation and convection. Heat storage becomes more essential as the dependence of the building on solar gains increases. If the building is only solar tempered, which means that the solar contribution is relatively small (usually less than about 40%), solar gains primarily offset the needs for daytime heating. Some heat storage will take place, but requirements for building heat at night and during cloudy periods are met primarily by auxiliary sources. In a well designed passive solar building the situation is quite different. Typically, no auxiliary heating is required in sunny winter weather. This means that all of the nighttime heating must come from heat stored within the building. Normally some auxiliary heat is still required, but it is needed only during cloudy periods when there has been less then full sun for one or more days. The need for auxiliary heat increases gradually as the heat stored in the building is gradually depleted. In no small part, the economy of passive solar heating systems from the dual use of most of the construction and furnishing materials. Window serve for light and view as well as for solar gain. Heat is stored in ordinary walls, floor, and indeed in all of the materials of the building. Although one may alter the construction techniques of the building to enhance the amount of heat storage available, in almost all cases heat storage serves multiple functions. The designs used for Passive Solar Space heating can be divided into five types as follows; i-) Direct Gain ii-) Trombe or Water walls iii-) Thermosyphon Collector iv-) Attached Sunspace v-) Roof ponds Direct Gain: Direct gain is by far the most widely used passive solar strategy. It occurs to one extent or another in almost all passive solar buildings. It occurs with all windows, whether they are south facing or not, and storage of most of the heat associated with the solar gains occurs whether we plan for it or not. If the materials of the building interior are very lightweight, heat storage might be quite temporary, and transfer of the heat to the air in the room may take place quite soon. In more massive materials, the heat diffuses to the interior and is returned only at a later time when the room temperature drops, allowing for a reversal of temperature gradients so that the heat can rediffuse slowly to the surface. The short-wave solar radiation has entered the south facing window and then is turned into heat at one or another of the building's internal surfaces, one of three actions occurs: (1) the heat migrates into the material, (2) the heat is transferred to the XIVroom air by convection, or (3) the heat is reradiated as infrared energy to all of the surfaces within the room that can be viewed from that location. Most of the energy that flows outward from the surface does so by infrared radiation with convection to room air being the smaller component. Thus each surface in the room is continually bombarded by infrared radiation from every other surface within view. Doubly-glazed window is used to reduce the loss of heat from the room to outside air and the windows are covered by insulation in the night for the same purpose. The heated house tends to get very hot in the day unless storage mass (in the form of bare massive floor or wall or otherwise) is provided in the room. The oscillations in the temperature of air are large. These oscillations are reduced by providing a thermal storage media either under the floor or in the north wall. Trombe or Water walls: In spite of the storage provided in the direct gain concept, the fluctuations in the room temperature are usually higher than tolerated by man for desired comfort level. A more effective method for reducing the swings in the room temperature is to introduce a thermal storage wall between the direct solar radiation and the living space. The sun's energy in this concept is introduced into the room in an indirect fashion as a result of convection and longwave radiation emitted by the thermal wall which gets heated due to the absorbed energy at its surface. A massive thermal wall of concrete or masonry usually facing south, suitably blackened and glazed greatly reduces the temperature swings in the room air. Doubly-glazed dark south wall gets heated up by the sun during the day. The air entering the space between the wall and the glass gets heated and returns to the living space through the vents provided in the massive wall. The heat input into the room can be reduced by adjusting the flow of air through dampers. The glazing over the wall is covered by insulation during off sunshine hours and the dampers closed to reduce heat losses to the ambient. The heat conducted through the wall gets transferred into the room by radiation and convection all the time. Attached Sunspace: This concept proposed by Balcomb (1978) represents a marriage of the concept of direct gain and indirect gain. The living space has a thermal storage wall on the south side; attached to the south wall is space enclosed by glass. The glass enclosure called sunspace receives heat by direct gain, while the living space receives heat by indirect gain, through the thermal storage wall. This concept provides a pleasant sunspace, which may be used for growth of plants. Moving insulation over the walls of the sunspace improves the performance considerably. Thermosyphon Collector: Solar radiation passes through the glass and is absorbed by the black painted absorber plate. A thermosyphon collector can be built either into the south wall of a house or at a level lower than the house. When built into a south wall, the collector delivers heat to the house by a continuous pattern of natural air movement called a convective loop (or thermosyphon). The air in the collector rises as it is heated and enters the room through a ceiling level vent. This movement creates a draw that pulls air into the collector through its floor level vent. A south wall thermosyphon collector is often not linked to a storage element. However, when the collector is placed below the house, it can be hooked up with a rock storage bin. Here again, the heat circulates naturally, but much of it is absorbed and stored as it passes through the bin. xvRoof Ponds: Containers of water on the roof of a house can also be used to collect and store the sun's energy. A container tilted at 45°-60 ° would have the best exposure to the winter sun, but supporting and confining a large mass of water at such an angle is a formidable task. More feasible are horizontal rooftop collectors, which confine the water by exploiting its propensity to lie flat. The water can be kept in shallow pans or in plastic bags upon sheet metal decking and supported by concrete walls or thick wooden beams. The solar heat collected in such roof ponds is radiated directly to the rooms below. Also, roof ponds are extremely well suited to the purpose of summer cooling. In this study, the flow in a Trombe wall channel has adiabatic horizontal walls and isothermal side walls was simulated, and streamlines, isotherms and flow patterns were obtained. The Trombe wall channel which is one of the passive solar heating design systems is formed by a window on one side and a massive wall on the other side. The massive wall absorbs the solar energy and releases part of it at constant flux to the air which enters into the channel through bottom vents, cooled down inside the heated zone. The circulation of buoyancy-induced convective flow heats the adjacent zone. It is clear that, the channel has key function for determining the best design for using solar energy effectively. Therefore, the study was focused on the channel. H y Tg: The temperature of the glazing Tw: The temperature of the wall Defining the channel height to channel width ratio as the aspect ratio(A) was selected 16.5. Since the Grashof number in the range of 3xl06 and lOxlO6, the flow has been assumed to be laminar. The mass, momentum and energy conservation equations which have been defined as buoyancy-induced flow are introduced below : âx ât _ - + - = 0 âi. âj XVI»2"> -g[l-/?(Tw-T)] âı âf l
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