The Facets of Heat Transmissions through Building Elements - Term Paper Example

The Calculation of Heating and Cooling Loads By (Name) Institution Instructor Class/Course City Date Executive Summary The building sector affects the society in various ways: economically, socially, naturally, and built environmentally. In a more direct or indirect manner, the various building activities including designs, construction, use, refurbishments, as well as demolition of the buildings affects the environmental performance differently. In bringing environmental issue into the context, it is true that a feature of environmentally sustainable is not only comfortable to occupy, but also consume small amount of energy. Studies argue that the major goal of sustainable design involves reducing or ultimately eliminating depletion of natural resources and degradation of environment due to the infrastructures and facilities made by man. Although various factors are barriers, this situation calls for a better ways of approaching the building activities that are environmentally sustainable. Building policies plays critical role in reducing environmental impacts although little research has been done as far as this sector is concerned. These policies should focus on codes for environmental sustainability of building designs that establishes better planning practices, designing as well as constructing buildings with environmental concerns of the impacts of the build structures (Davies, 2004). This paper is divided on its aims that consider the facets of heat transmissions though building elements like walls, ceilings, and floor. Secondly, the paper looks into the solar geometry elements in the analysis of the solar effects during the day as well as expressing the knowledge of the solar radiation and its penetration to the building surfaces. Finally, the paper examines the heat transmission through the windows. Introduction The criterion of environmentally sustainable design is based on five facets parts. The first aspect involves efficient energy approach in building design and means of optimizing the performance of buildings as far as energy is concerned. The second aspect involves the efficient water selection fittings and components that reduce wastage during building process. The design also focuses on protection of the environment based on the chosen materials and analysis of their impacts on the built structures. The fourth part looks into the internal qualities of the design and links to the environment as far as air quality, heat comfort, lighting etc. Finally, the concern of the design is about the green elements like technologies and associated environmental benefits. A sustainable building design represents the principles of sustainable development. To achieve this, the buildings must be designed so that their heating and cooling loads are as low as possible (Vassigh, et al. , 2013). One of the significant drivers of this aspect is the temperature difference between the outer and the inner surfaces of the building. The determination of this temperature difference is helpful in choosing building materials and to design an economically, yet aesthetically pleasing buildings. This study is founded on the following points of study: i. Heat transmission through the building elements such as walls, ceilings, floors etc. ii. Description of the solar geometry for the calculation of the sun’s location during the day, at any location of the earth iii. The knowledge of the solar radiation for calculation of the heat transfer through building surfaces (role of thermal radiation) iv. The variation of the solar loads with the diurnal cycle v. Heat transmission through windows Heat transmission through the building elements The principle guiding the transmission of heat through buildings is guided by the thermal qualities of the building itself in terms of the processes involved in the transfer of heat energy into and out of the building. According to Davies (2004), in this process, for an acclimatized building, cooling and heating load is estimated. However, in a building lacking conditioning, variations in temperature within the building are determined in a distinct timeframe to help in other periods. The quantifications discussed in this segment of the paper is significant in determining the ultimate importance of the design of a building. It is also critical for the improvement of the designs in a sustained gain of efficient energy within the building with sustained environmentally comfortable situations. However, as many people luck the required quantification, the passive solar architecture becomes a very rare knowledge and skill among many architects. Based on the arguments of Underwood & Yik (2004), the inquiries made by most people revolves around the level of energy preservation and temperature reduction in balancing the expenses associated with the change of design. In the same way, designers examine criteria of relative performances of the building choices as better ways. This means that the skills and acquired knowledge for estimating design performance is significant for the passive solar buildings. There are several heat exchange processes that goes on normally between a building and the surroundings. Conduction is the process by which heat travels through solids from the source (Vassigh, et al. , 2013). In this case, therefore, by conduction, heat is transmitted across material elements like walls, roofs, floor etc. The processes of heat transfers through fluids and air are convection and radiation respectively. The transmission of heat also involves different surfaces through the process of convection and radiation (Davies, 2004). More than that, the radiations of heat from the sun disperses through materials that are transparent like the windows and absorbed afterwards inside the building. Evaporation of water may be the end result of the cooling effect, but human presence and the lighting system in the building may add to the heat. According to the arguments of Davies (2004), metabolism processes in the human body during rest produces heat that is exchanged into the surrounding for temperature balance. The feeling of the cooling effect comes with the loss of heat from the body. However, gaining heat in the body leads to transpiration, thus the circulation of air in the building is very crucial for the comfort of the body. As argued by Wilson & Piepkorn (2008), the thermal performance precipitating the elements of heat transfer of a building relies on certain issues. The other factor in this prospect is the properties of the materials used in terms of their density, specific heat, thermal conductivity, and transmissivity, among others. The third factor is the weather information regarding the solar radiation, ambient temperature, speed of wind in the area, humidity, among others. The fourth is the data usage of a building in terms of the internal gains because of those who live inside, lighting and equipment, exchanges of air and many other related factors. These factors affect the thermal ability of a building and many studies have been done relating to these segments using appropriate analytical tools. Analytical tools (methods) like steady states methods, as stated by Wilson & Piepkorn (2008), the dynamic methods, and correlational methods, use simple techniques to estimate the performance of the buildings. Consider the chart below representing the factors mentioned above that determines the thermal performance of a building. Figure 1: the thermal (heat) transmission through the building elements The processes of heat transfer that take place in a building, such as convection, radiation, and conduction are better understood by considering a wall exposed to solar radiation and the other surfaces facing a room (Underwood & Yik, 2004). When the solar radiation fully falls on the wall from the outer surface, heat is reflected partly to the environment and partly absorbed into the wall and converted to heat energy. However, through the aspects of convection and radiation, some heat is lost to the environment afterwards (Wilson & Piepkorn, 2008). The solar geometry and the position of the Sun According to scientists, the major source of heat and light is the sun in the solar system. The composition of the sun is believed to be hot gaseous elements, especially at the center. Through fusion reactions, the heat is transmitted to the surrounding bodies like earth. As argued by Duffie & Beckman (2001), the sun is roughly spherically shaped, about 1.39x106km in diameter and about 1.496x108km from the earth. The plane linking the sun and earth is subtended at an angle of 320 to the surface of the earth. However, Anink (1995) records that this link makes the sun’s heat are directly transmitted to the earth’s surface. The solar radiation is directed to the surface of the earth after being weakened, reflected and scattered in the earth’s atmosphere. In general, before the heat from the sun reaches the earth, it undergoes a series of dispersion and interruption of its greater intensity. Nevertheless, there are majorly two kinds radiations experienced in this case as described in the following outlines: i. Beam radiation (received directly without directional interference) ii. Diffuse radiation (received after scatter, reflection, and directional interferences). iii. A combination of the two is the total radiation, normally known as the global radiation. The sun’s position on the celestial sphere can be estimated by knowing the angle of the right ascension and the declination. Consider the figure below of the solar geometry and the position of the Sun: Figure 2: The solar geometry and the position of the Sun SUN (Ø 1.39 X 106 KM) EARTH (Ø 1.27 X 104 KM) 320 1.496 X 10KM ± 1.7% As argued above, the earth is spherical with an approximated diameter of 1.27x104km. By rotating, the earth revolves around the sun in an elliptical orbit, making one complete revolution in one year. However, the rotation of the in the axis takes one day. According to the facts recorded by Irvine (2012), the amount of heat energy from the sun is constant outside the earth’s atmosphere. This energy is known as the Solar Constant. This energy is only transmitted based on the position of the earth to the sun with a value approximated to be 1367 W/m2. Solar radiation and role of thermal radiation According to Irvine (2012), the solar radiation incident on the earth’s atmosphere is relatively constant. However, the radiation on the earth’s surface varies widely due to a number of factors. The main factors are the thermal absorption and reflection. These two aspects cause atmospheric variations in water, pollution, and clouds. They also cause latitude and seasonal variations during the day. These factors affect the solar radiation on the earth’s surface and causes changes on the magnitude of the solar effects felt on the earth’s surface. These changes, as argued by Irvine (2012), however, does not only cause disparities in total energy received, but affect also the spectral content of the light and the angle from which the light is incident on a surface. Based on the facts received from KurowskI (2014), the local effects seasonal and weather variations cause thermal variations in specific latitudes. For instance, the desert regions tend to have lower variations due to local atmospheric phenomena such as clouds. Equatorial regions have low variability between seasons. However, the key area of interest on this study is the solar radiation on a building surface, such as on tilted surface, unshaded surface, and shaded surface. Radiation on surfaces: Tilted surfaces The external surface of buildings that receives heat from the sun is tilted with the exception of the level rooftop, which has a plane surface. Nevertheless, it is important to approximate the heat on such surfaces based on facts determined from on the plane surface. According to KurowskI (2014), a tilted surface gets the following heat from the sun: i. The transfer of heat directly from the sun ii. The dispersed heat from the sky elements iii. The reflected radiation from the neighboring buildings and objects According to KurowskI (2014), the Earth's axis of rotation is tilted 66.5 degrees with respect to its orbital plane around the sun and its axis of rotation is inclined 23.5 degrees perpendicularly to this plane. The tilt of the Earth affects the angle between the sunbeam and the normal over a surface (Anink, et al. 1995). The sun angle affects the flux density of heat radiation incident on a surface. The declination angle corresponds with the angle separating the solar noon rays of the sun and the equator. The Earth’s declination angle has limits that correspond with the seasons: Summer solstice: + 23.45 degrees. KurowskI (2014) also states that during the summer solstice the sun is directly overhead (90 degrees) at the Tropic of Cancer and has an angle of 66.5 at the Equator and is at the horizon at the Antarctic Circle (66.5 S). Below the Antarctic Circle, it is dark 24 hours a day. Above the Arctic Circle (66.6 N) there is sunlight 24 hours a day. Shaded surface For a shaded surface, the radiation incident falling on it varies based on the shading type. The difference in the shading type complicates its estimation (Vassigh, et al. , 2013). Conduction As argued above, heat transfer through solid objects is conduction. Now, the extent of the conduction of heat through element such as roof, wall or floor under a steady states, symbolized as Q cond = A U ΔT The equation for the conduction through the walls, roofs, ceilings etc. give result for the external composition of the building like walls, window, door, roof and the floor, to give the summary thereof (Vassigh, et al. , 2013). The movement of the heat in the building through conduction is the combination of the area and the U-value products of all the elements of the building multiplied by the temperature difference. Conclusion It is no coincidence that during building, proper appropriations, and analysis must be taken into consideration. The thermal effects on the building may have devastating results if at the initial stage, builders and architects lack the knowledge and respect for the impacts of the sun and its heat. The daily hours of solar radiations must be estimated as well as consideration of the global and diffused solar radiations. Therefore, buildings like assembly halls, bedrooms, bathrooms, cafes, restaurants, theaters, hospitals, kitchens, laboratories, and offices among others must be designed with the background knowledge of the solar heat (radiations) through the building. The internal gain of heat due to the occupants, the energy emitted by electrical appliances, lamps, etc. are all sources of internal heat must all be considered. References Anink, D., Boonstra, C., & Mak, J. 1995. Handbook of sustainable building: environmental preference method for choosing materials in construction and renovation. London, James & James Science. Davies, M. G. 2004. Building heat transfer. Hoboken, N.J., J. Wiley. http://search.ebscohost.com/login.aspx?direct=true&scope=site&db=nlebk&db=nlabk&AN=108191. Duffie J.A. and Beckman W.A., 2001.Solar engineering of thermal processes, 2nd Edition, John Wiley and Sons, Inc., New York. Irvine, P. J. (2012). Climatic effects of solar radiation management geoengineering. Thesis (Ph.D.)--University of Bristol, 2012. KurowskI, P. 2014. Thermal analysis with solidworks simulation 2014. Mission, KS, SDC Publications. OECD 2001, “Case Studies on Policy Instruments for Environmentally Sustainable Buildings”, OLIS Document, ENV/EPOC/WPNEP(2001)33. Organisation For Economic Co-Operation And Development. (2003).Environmentally sustainable buildings challenges and policies. Paris, OECD. Underwood, C. P., & Yik, F. W. H. (2004). Modelling methods for energy in buildings. Oxford, Blackwell Science. Vassigh, S., ÖZer, E., & Spiegelhalter, T. 2013. Best practices in sustainable building design. Wilson, A., & Piepkorn, M. 2008. Green building products the GreenSpec® guide to residential building materials. Brattleboro, VT, BuildingGreen. Read More