Güneş enerjisinden ısıtmada yararlanma

Abstract

ÖZET Dünyadaki tükenir kaynakların azalması neticesinde, bilim adamları doğada bulunan yenilenebilir kaynaklardan yararlanarak enerji tasarrufuna yönelik araştırmalara başlamışlar ve mevcut ısıtma sistemlerine yardımcı kaynak teşkil etmek üzere güneş enerjisinin kullanımı, bina ısıtma süreci içinde yer almıştır. Söz konusu uygulamaların Türkiye'de de başlatılması ve sıklaştırılması hem enerji tasarrufu hem de çevre kirliliği ve ülke ekonomisi açısından gereklidir. Bu sebeple güneş enerjisinden ısıtma sistemlerinin şimdiye kadar uygulanamama nedenlerinin araştırılması ve çözümlenmesi gerekmektedir. Bu çalışmada ilk dört bölümde güneş enerjisiyle ısıtma sistemi terminolojisi, ilk bölümde güneş ışınımına ait temel kavramlar, ikinci bölümde güneş enerjisiyle ısıtma prensipleri, üçüncü bölümde pasif sistemler, dördüncü bölümde aktif ve karma sistemler olmak üzere incelenmiştir. Daha sonra beşinci bölümde güneş enerjisinden faydalınalarak bina tasarımı, altıncı bölümde konuya ait Türkiye'de veya Dünya'da uygulanmış veya tasarlanmış örnekler, yedinci bölümde söz konusu sistemlerin Türkiye'de uygulanamama sebepleri ve son bölümde güneş enerjisinden ısıtmada faydalanmak amacıyla Türkiye'de yapılması gereken değişiklikler sunulmuştur. vii-

UTILIZATION FROM SOLAR ENERGY ON HEATING SUMMARY As the result of the energy crisis In 1970's, researchers have been started to Investigate renewable energy sources existing in the nature; utilization of solar energy is a part of this concept. Architects along with other energy consumers in industrial societies, have been called to develop more efficient solutions by using solar energy in building design process. In minimizing energy consumption in buildings and cities, designing of built environments which can provide control by making use of or providing protection against regional climatic effects without making a concession from the climatic comfort of user should be a top target. Related with that target, to minimize the energy consumption, architecturally the first approach has been to reduce the energy wastage in buildings; the second approach has been the utilization of the sun as a renewable energy source. For the time being utilization of solar energy has been investigated as an auxiliary system to minimize the energy consuming and to obtain the energy saving. Therefore solar heating systems should be planned with an additional heating source mostly based on consumable energy; but the aim should be the maximum utilization from the solar energy and minimum utilization of the additional heating source. With an annual population increase of around % 3, Turkey was affected more from the worldwide energy crisis m 1973 and encountered bigger problems compared to other countries. Although shifting of energy production to hydro-electric power plants has enabled Turkey, for the time being, to meet her demand for electric power to a large extent, particularly heating is still based on consumable energy sources and largely dependent on petroleum. Having a great potential on this area, Turkey should also utilize from the solar energy as a renewable source in the field of application like all the other developing countries in order to solve the energy problem; but there are still have some difficulties to reflect the required know-how on application. The purpose of this research is to examine these difficulties concerning solar heating applications in Turkey and proposing some solutions to order to solve the problem. But first of all the solar energy teminology is examined and explained.vüi.on the beginning chapters of the research in order to present the required knowledge. The energy in matter is difficult to use. More promising is the energy that is all around in the dynamic forces of nature: the wind, tides, waves, rivers, geothermal hot spots and the sun. The problem is that nobody has been forced to find the technological means to convert these natural energies into usable forms because it has been too easy to dig or pump the energy out of the ground. The problem is not a shortage of energy itself, but a shortage of technology for converting the energy that lies all around into useable forms. Energy conversion technology is the real issue, and solar energy is one of the brightest and most promising frontiers in energy conversion. In the first chapter of this research, solar radiation, heat, and some of the other forms of energy relevant to solar technology have been described. SOLAR RADIATION From the earth the sun appears to move across the sky in an arc, roughly from east to west, owing to the rotation of the earth around its north-south axis. In the northern hemisphere sunrise and sunset occur farther toward the south during the winter, but move northward in the summer as the sun travels in a higher arc across the sky and days become longer. This seasonal motion is due to the slight tilt of the earth's axis and earth's revolution around the sun. Because the solar radiation collides to the clouds, dust particules, air and water molecules after entering the atmosphere, a part of it practically scatters in all directions and the vapor on the top layers of the atmosphere absorbs another part of the solar radiation; but the rest reaches the earth without having any change on its direction and wavelength. As the result, the solar radiation reaches the earth on two different kinds: The direct solar radiation (Irj) is the short wave radiation that passes through the atmosphere without having any effect of the absorption and collision and therefore reaches the earth without having any change on its direction and the wavelength. The diffused sky radiation (1^) is the part of the original direct solar radiation in the atmosphere that reaches the earth after diffusing in all directions because of the scattering effects. - ix -The terms and computations based for the solar radiation calculations are solar constant and the distance between the earth and the sun, earth-plane-solar angles, the permeability of the atmosphere, meteorological factors, and the solar time-local time. The calculations of the global solar radiation consisting of the two components such as the direct solar radiation and the diffused sky radiation reaching on the horizontal plane are usually given related with the meteorological data such as the solar radiation period, relative humidity, atmospheric pressure, temperature and the cloudiness. The ratio of the diffused sky radiation (the ratio of the diffused sky radiation on the horizontal plane to the global solar radiation) is generally given as the function of the limpidity indices (the ratio of the global solar radiation on the horizontal plane to the solar radiation on the out of the atmosphere) or the relative solar radiation period (the ratio of the solar radiation period to the daytime). If the global solar radiation and the daily diffused sky radiation is known then the daily direct radiation can be calculated by subtracting the global solar radiation from the daily diffused sky radiation. The optimum slope of a plane located with a fixed slope to gain the maximum solar radiation is calculated for a specific period of time; the selection of this period is related with the kind of the energy requirement and the requirement quantity that will be compensated by the solar energy system. The slope of an optimum plane is considered for the whole year if there is a continuous need of hot water or electricity, for the required months if there is only heating and cooling requirements and if the total requirement is planned to be compensated by the solar energy system then the slope is determined for the critical month. HEAT It is difficult to consider the thermal behavior of buildings and to design for solar heating without understanding the nature of heat and how it flows from one place to another. Heat and temperature are easy to observe but are rather difficult to describe and fully understand. For example in the solar heating field typically spoken is the storage of heat or stored heat but, thermodynamically, heat cannot be stored. Rather, heat is - x -an Interaction and ceases to exist once an energy-transfer process stops. What is stored is internal energy not heat. The amount of internal energy an object contains is a grand total of all the kinetic and potential energy of all of the molecules in the object. Temperature is obviously related to internal energy, yet it is not measured in units of energy as heat is. But temperature is the average energy indicating the kinetic energy of the molecule whereas the internal energy is the total energy including both potential and kinetic-energy effects. There are three basic ways in which heat can be gained, lost, or transferred from one object to another. These are conduction which is simply the flow of heat through an object or material and it occurs as energized molecules transfer energy to their less- energized neighbors, convection which refers to the transfer of heat by a moving fluid or radiation which is the transfer between different bodies of heat energy by infrared or visible light due to differences in temperature. UTILIZATION FROM SOLAR ENERGY ON HEATING As stated above diminishing of the consumable sources and the cost increase of these sources, and the pollution caused by the use of the consumable sources and related with this the cost effect of the solutions to prevent the pollution has forced the researchers to search for new renewable sources and as a result of these researches the utilization from the solar energy on heating has been investigated. There isn't any production cost for solar energy but the maintenance cost of solar energy on heating and climatization depends on the maintenance approach of the system. Basically there are two approaches on heating and climatization: first approach is defined as the active system consisting of collector-storage-distribution units for the heating and climatization systems, and the second approach is defined as the passive system which is the realization of the building as a kind of passive heating and climatization system by gaining optimal values related with the utilization from the solar energy to the building parameters such as orientation, building form and building shell. There isn't any definite classification of the active and passive systems; the classification differs on various researches. On this research the active and passive systems have been classified according to the fuel that the systems are consuming and the system has defined as the active system if any kind of consumable fuel has been used in any part of the system; otherwise the xl -system has been called passive. The solar energy heating system consists of collectors, absorbents, storage units, distribution elements and adjusting units; but mainly the basic two parts are the collectors and storage units, the rest are the sub-parts of the system. Therefore the basic topics to be searched are collecting and storing solar energy. Utilization from the building as a solar energy collection element is the simplest method to be used in solar energy collection process. In this case the kind of the glass to be used, the color of the building to be painted, the location the building is oriented and finally the building shell and form have an important role in solar energy collection. The other method is to utilize from the collectors to collect the solar energy. There are basically four kinds of collectors to be usedrliquid type flat- plate solar collectors, air type flat-plate solar collectors, vacuum collectors and the concentrating collectors. Air type and liquid type flat plate collectors are used mostly in buildings compared to other kinds of collectors. Flat plate collectors consist of a transparent cover, air space, absorber plate, insulation and the frame. Similarly utilization from the building as a solar energy storing unit is the simplest method to be used in solar energy storing process. In this case the kind of materials to be used has an important role in solar energy storing. The other method is to install heat storage units either inside or outside of the building to store the collected solar energy. Liquid storage units are used for the liquid type flat-plate solar collectors and rock or phase change storage units are used for air type flat-plate solar collectors. These are the basic and practical heat storage methods used for utilization from the solar energy in heating; researchers are carrying on their investigations for new technics such as the salt ponds, annual heat storage and the chemical storage methods for the storage of the collected solar energy. PASSIVE SYSTEMS A passive solar approach to building design involves more than maximizing solar gains. It is a total design approach and thus demands the interaction of many factors including best use of the physical site conditions, control of the complete xii -thermal envelope of the building, cost considerations, thermal and visual comfort, and the life style of the occupants. The approach should be flexible and good design will result from a balance between thermal and client specified criteria and not from imposing a highly efficient system with little regard to user requirements. The passive solar home makes use of the materials from which the dwelling Is constructed to capture, store and distribute the solar heat to its occupants. High heat capacity material (such as brick, concrete, stone or water) absorbs this solar energy as It enters the house and stores it in the form of heat. The living spaces of the home are carefully arranged so that they are in direct thermal contact with this store, allowing these spaces to be heated directly without the expense of special plumbing or forced hot air distribution systems. Passive design require consideration of solar and heat flow in every detail and component. Floor plan layout, circulation patterns, window location and the selection of wall and floor materials, all affect how well a passive design will work. The entire house is a solar energy system with many of its components now having dual functions: both the traditional function of providing an enclosure, and the solar functions of collecting, storing and distributing heat. Windows not only let in light and allow a view, but collect heat as well. Walls which subdivide and enclose space can also store and radiate heat. Components whose functions were primarily structural, special or aesthetic may double as solar heating mechanisms. The first step in passive solar design is to determine the design parameters to obtain the optimum solutions in order to minimize the energy consumption. These above mentioned parameters are basically classified on four groups such as location, orientation, building form and building shell. Also other parameters and control systems such as solar control, wind control and humid control are added to these above mentioned parameters according to the requirements of the problem. The passive systems are classified mainly as direct gain systems and Indirect gain systems. The diffusing and non-diffusing systems can be considered the sub titles of the direct gain system and Trombe walls, water ponds, roof ponds, attached sun spaces and thermosyphoning collectors can be considered the sub-titles of the indirect gain system. - xlliACTIVE SYSTEMS Like the passive systems, a typical active solar heating system involves more than Just an array of solar collectors and a heat storage unit. Pipes or air ducts are needed to carry the heat transfer fluid (air or water). Pumps or fans are required to circulate the fluid. Some provision is needed for backup or auxiliary heat when sunlight alone is not enough to keep the building warm. Automatic valves or dampers are needed the path of the fluid. Heat exchangers, filters, vents, and other miscellaneous parts are required. To coordinate all of this equipment and make the decisions as to which device to turn on and when, a control circuit is needed, along with thermostats and other sensing devices. The active system can be divided into two main group according to the fluid in which heat is transferred; those are air type solar heating systems and liquid type solar heating systems. The elements of the active system consists of the basic system elements, fluid-control elements, system-control elements, protective components, and other available equipments. In active system design, systematic procedures can be used to define the modes necessary for an active solar system. Once the modes are determined, a simple equipment layout can be sketched. Next, sensors and controls can be specified and switch the appropriate equipment on the appropriate times. At this point a plan of the entire system can be drawn up. In other words there are four essential phases in the design of solar heating systems:specification, equipment layout, controls design and physical design. As stated above, a well-balanced design between the consumption of the human requirements and the utilization from solar energy is realized by a specific systematic. This systematic consists of the two integrated systems such as the active and passive systems. In this systematic, the utilization from the solar energy should be solved by obtaining the maximum performance from the indirect passive systems and then integrating with the direct passive systems the whole passive system should be completed with the necessary active systems at the minimum level. The building types to be utilized from the solar energy can be classified in five groups such as single houses, multi-story buildings, commercial buildings and industrial buildings. The fifth group is classified as the retrofitting of the existing buildings. The - xlv -applied or designed system models are divided In two groups In this research to make a comparison; and In the first group the applied or designed system models In the world has been presented on the sixth chapter. These samples are also divided into three groups such as multi-story buildings, clustered housing and single houses. In the second group the scientific works and design and application processes executed in Turkey has been presented. THE EXISTING PROBLEMS CONCERNING SOLAR ENERGY APPLICATIONS IN TURKEY On the last two chapters, the reasons for the lack of solar applications in Turkey have been investigated and some solutions have been proposed. The first reason is basically the heat loss. As stated before, the first condition in utilization from the solar energy is to prevent the heat losses and in Turkey both the bad quality of materials used In constructions and the labor cause the heat losses and in addition to this problem the Insulation of the buildings has been omitted by the contractors. The second reason appears to be the economic factors. Both the cost of the solar energy systems and the measures to be taken to prevent the heat losses Increases the initial cost of the system. The third reason is the incorrect orientation of the buildings and the cities and the other lacking reasons are the state support, interest of the designers and applicants, and the constitution of the public opinion. In order to solve these problems and utilize from the solar energy, the first step should be the revision of the existing regulations because the existing regulations are not sufficient for the utilization of solar energy; besides they are not even sufficient for minimizing the energy consumption. The other steps to solve the problem are the economical, application and design precautions that should be taken. Turkey has the potential to generate information at the highest level on the subject of most rational utilization of energy both In brand-new and existing buildings, and in addition to those problems discussed above, her most Important problem today is the rapid population Increase and the consequent rapid, unplanned and mostly illegal construction activities and urbanization combined with the impossibility to enforce the regulations and standards regardless of how perfect they may be. - xv