Environmentally Sustainable Buildings - Term Paper Example

Environmentally Sustainable Buildings Student University Executive summary Houses are designed so that the occupants can be comfortable at all times. In this modern era, the environment has been of great concern. This is because; human activities are contributing to a larger percentage of the environmental pollution as well as the environmental deterioration. Since the environment supports life in most aspects, it is therefore important to ensure that the environment is always conserved. The design of houses in the construction industry has been improved to incorporate all the aspects of environmental conservation as well as using minimum energy. A sustainable house will ensure that the future generation will enjoy all the facilities the present generation is enjoying. This particular house should have a ample ventilation, a favorable temperate, adequate air changes, favorable humidity, enough lighting and so many other factors that would ensure that the occupants are comfortable. Since achieving these conditions needs design materials which need to be included, the cost of such materials together with their specific properties have to be determined so that the best cost which should be the minimum cost can be determined. The effect of the materials to be used to the environment has to be investigated so that the materials to be used have a negligible negative impact to the environment. It is also important to determine the inner and outer temperatures, this will help in choosing materials that will ensure that their temperature is kept at a minimum level. At the same time, the appearance of the house should be pleasing all the time, therefore, in the design, the materials with the best aesthetic properties must be carefully selected This indicates clearly that in coming up with the environmentally sustainable buildings, the energy to be used, the cost of the materials, the effect of the building to the environment as well as the effect of the materials to be used on the environment have to accurately investigated and ultimately determined so as to achieve the intended purpose of the buildings. Environmentally Sustainable Buildings Introduction The amount of heat in a house dictates the level of comfortability of the occupants. if the heat is too high, the inner temperatures will be severe hence causing sweating to the occupants who may lose a lot water in the process, they will spend a lot of money to acquire equipment such as fans to try to reduce the heat in the house which is very uneconomical. On the other hand when the heat is too low, the occupants will lose a lot of heat energy from their bodies, this will cause continued shivering to the occupants which may force the occupants to acquire heaters in the house. It is therefore important to ensure that the heat in the house is kept at a reasonable level that will ensure that the occupants lead a normal lifestyle without any need of acquiring extra equipment. The temperature difference between the inner and outer surfaces must be kept as minimum as possible and also it should be kept constant, to ensure this happens, the mechanism of the heating load and the cooling load must be clearly checked to standard rates so that the temperature is kept constant at all times. Heat is transferred through conduction, convection and radiation. Heat transfer through solids such as walls, floors and ceiling is majorly by conduction. In this process, heat is transferred from a region of higher temperature to a region of low temperature through a given solid. In fluids (liquids and gases), heat is transferred through convection. In this process, the density of the fluids enables heat transfer majorly upwards and downwards. When the temperature is high at one point, the density of the fluid is lower at that point hence the fluid rises, transferring the heat to the cooler parts while at the same time, the more dense cool fluid, replaces the rising less dense fluid and the process continues. This process of convection majorly takes place in the house, whereby, when one room of the house is heated, the heat may be transferred to the other places in the room by the rising air. Lastly, heat transfer by radiation, does not require any medium i.e. it does not require the solids, liquids or gases for heat to be transferred, it only requires the space. The heat transfer through this process is mainly sideways from one body to another enabled by the temperature difference between the two bodies and the solar radiation downwards as well as the lighting equipment in the house. The amount of heat in a house can be influenced by a number of factors, the common factors that influence the amount of heat in the house may include: The number of occupants; human beings experience metabolic processes in which heat is being released to the environment while some of the energy is used for work. When the number of occupants is many, then the amount of heat released to the environment is high hence high temperatures in the house while when the number of occupants is few then the amount of heat released to the environment is low which results to low temperatures in the house. Using lights and equipment; every house must be equipped with artificial lights to be used most especially at night, this uses either the common bulbs or fluorescent tubes, these use electricity to produce light and some significant amounts of heat, as a result, the room temperature increases and depending on the number of the light equipment; the higher the number of equipment the higher the amount of temperature gained and vice versa. The house design; a house with a few number of rooms as well as a small house space, will require less heat energy to increase the temperature in the room than a house with a many rooms and a larger house space. This is because, when the house has few rooms, the heat loss is minimal and at the same time, the heat transfer from one point of the room to another point of the room is effective since the distance covered is smaller than when a house with many rooms is considered. The available ventilation; in most cases, this refers to the natural ventilation that involves all the house openings including windows, doors and the permanent openings in the house that ensure that the heat gained in the house is lost to the environment. If the sizes and the number of the openings are increased then the heat loss is high and vice versa. Therefore, to ensure that the heat in the house is kept at a reasonable constant rate then standard depending on the size and the location of the house openings should be used. Materials used for the house construction. When using materials with insulating properties, then the heat lost will be kept a minimum in the house, in that regard, the house temperatures will be elevated using the minimum heat energy. The mentioned factors are the most commonly used in the design of buildings to ensure that the occupants are comfortable as well as ensuring that the environment is safe and less energy is used, therefore, a proper evaluation of all the factors has to be done to ensure that the house design has the most favorable properties . Transmission of heat through building elements Heat transfer through building elements such as walls, floors and ceilings can take place through the processes of conduction, convection and radiation. A summary of the various heat transfer processes can be illustrated in figures below; Figure 1; heat transfer processes between the building and the outer environment Figure 2: human heat exchange to the inner environment Figure 3: heat exchange processes experienced in a wall To determine the quantity of heat transferred through these processes different formulae are used. These formulae are considered below with their respective processes. Conduction process Conduction is process through which heat is transferred through solids. The heat is transferred from a point in the solid experiencing a high temperature to a point in a solid experiencing a low temperature. The solid molecules are compact and their vibrations are minimal. These takes place between walls, floors and ceilings when one side of the components has a lower temperature than the other side of the building component. Because of conduction, the inner side of the wall that receives direct solar insolation will get the heat energy and its temperature elevated. On the same note, the temperature on either side of the floor will be controlled by the temperature of either side; this applies to the ceiling of the roof. Therefore, the materials used on these buildings elements should have the properties that will enable them transfer a favorable quantity of heat which is neither too high nor too low. To determine the quantity of heat transferred by conduction, the formulae below is used. Where; A simplified formula for determining the heat transfer by conduction is written as; Where; It is important to note that the amount of heat transferred through the wall is influenced by various factors. The wall direction in relation to the coming solar insolation; if the wall is in the direction of the incoming solar radiation, the amount of heat transferred through the wall will be higher than when the wall faces away from the incoming solar radiation. The material that is used to construct the wall, different materials have different rates of thermal transmittance, material with high transimattence will lead to high heat transfer rates while those materials with low transmittance rates will result to low heat transfer rates. Time of the day; the amount of heat transferred through the wall and the ceiling will also depend on the time if the day, in that when the maximum solar insolation is experienced, i.e. when the sun rays are in the position directly above the building, the outer surface temperatures are higher that the inners surface temperatures. The high temperature gradient will result to a very high heat transfer rate during this time of the day, during the early morning hours, when the sun has not yet risen, the temperatures inside the house are higher than the temperatures outside thus heat is lost to the environment, at this time the transfer is also high. Therefore, when calculating the heat transfer through the walls and the ceiling the factor of the time of the day must be considered . The season of the year. In regions far away from the tropics such as South Australia, the length of the day and night depends on the season of the year. During summer, the length of the day is longer than the length of night, as a result, a lot of solar insolation rates is experienced during summer leading to very high outer surface temperatures thus the heat transfer rate is very high at this time. On the other hand, during winter when the night time length is longer than the day time length, the time of solar insolation experienced at this time is therefore minimal which results to higher inner surface temperatures due to the energy released by the occupants and the equipment and a lower outer surface temperatures, as a result of these, the heat transfer rate is also high and more heat is lost from the house. Convection process Heat transfer through fluids (liquids and gases) is called convection. The main principle applied in this case is the change in density of the fluids in that warm fluid has a low density, therefore it rises and then replaced by a cold more dense fluid. In buildings, heat transfer by convection takes place on three main surfaces which include; the walls, the ceilings/roof and the floors.The two most common convection types experienced in buildings is the free convection and the forced convection. Free convection involves the motion of fluid due to density changes thereby transferring heat while the forced convection involves movement of fluid due to external forces such as wind. The two processes could take place independently or simultaneously depending on the location of the building and the direction of the winds. Since the occupants need some reasonable level of comfort, it is therefore necessary to determine the heat transfer rate by convection process; this can be determined by the formula: Where; Radiation process Heat transfer by radiation does not require any medium. It mainly depends on the temperature difference between two parallel surfaces. The heat transfer majorly takes place sideways and downwards in a given place. Therefore, in this case, the distance between the surfaces involved and the sizes of the surfaces are critical in determining the heat transfer by radiation. When the distance between the surfaces is small then the amount of heat transferred by radiation is high while, when the transfer of heat is minimal, then the distance between the two surfaces involved is very high. On the other hand, when the sizes of the surfaces involved In the radiation are high then the amount of heat absorbed or emitted is very high, if the sizes are small then the amount of heat absorbed or emitted is minimal. Therefore, to ensure the comfortability of the occupants, then the sizes as well as the distances between the objects and elementshas to be properly designed to ensure that a reasonable heat transfer by radiation takes place and that a favorable temperature is maintained in the building. To determine the heat transferred by radiation, the following formula is used; Given; Where; In some cases, some of the building parts such as the roofs and some of the walls may be exposed to the atmosphere which receives constant solar insolation. In this case, it is important to consider the heat exchange between the building and the atmosphere. The formula used below; Where; represents the temperature of an equivalent atmosphere. In this case, it is therefore important to come up with equations correlating the ambient air temperature and the sky temperature. Some of the equations that are used include; Given; Where; Applying the above formulae the radiation can be comprehensively accounted for, within the building and between the building and the atmosphere. In the design of buildings, the cooling of the building is taken into consideration; in this case, the processes of ventilation and evaporation contribute to the cooling of the house. Evaporation process needs heat, this heat is important in removing the water of vaporization from aqueous solutions, this water removal increases as the temperature and the wind speed increases in a given area. This evaporation process causes a cooling effect in the buildings and it depends majorly on; The external atmospheric pressure; the lower the external pressure the higher the rate of evaporation and vice versa. The surface area of the water exposed; a larger surface area exposed results to high rates of evaporation and vice versa. The rate of evaporation is higher at high temperatures and low at very low temperatures. Wind speed also influences the rate of evaporation experienced, when the wind speed is high, the rate of evaporation increases. The ventilation process is majorly determined by the number and the sizes of the openings in the house and the air exchange rate allowed for in the design. When the openings to the house in the form of windows and doors are large and many then it means that the cooling effect is very effective. On the other hand when the allowed air exchange rates are high, the the cooling effect is also very effective. In order to fully understand the heat transfer process, some examples will be solved South Australia as the place of reference. The month of September Conduction process The formula used is; House dimensions:, Therefore Assuming the house building material as wall to be dense concrete then In September; Thickness of the dense concrete wall, Then; Convection process Formula used in this case; Then; Radiation process The formula used in determining the radiation process is as below; Given; The values; Then; Solar Geometry elements The solar system consists of the sun, the planets, the meteors, comets, the moon and so many other elements. Our home the planet earth is the third planet on the universe and it is the only planet known to support life. The planet earth is spherical in shape and is held in position by the sun’s gravitational pull. Mercury is the smallest planet and the planet nearest to the sun while Jupiter is the largest planet. Pluto is the planet that is furthest from the sun. The planets move around the sun in their own orbits. The planet earth orbits around the sun once in 365 days. Its axis of rotation is tilted at an angle of 23.50 to the normal plane. Due to this, the sun’s elevation on the surface of the earth varies from time to time. The path of the earth around the sun is elliptical, in that there are times of the year when the earth is nearer the sun then other times. This brings about the four seasons, the spring, summer, autumn and winter in which the amount of solar radiation received on the surface of earth varies from one region to another. The position of the sun at specific times is very important to determine since this influence the temperature on the earth’s surface. When the earth is very far away from the sun, the day lengths are shorter than the night lengths, in such cases, the solar insolation received on the surface of the earth is minimum which results to very cold conditions on the surface of the earth especially on regions far away from the tropics. On the other hand, when the earth is very near to the sun, the daytime lengths are longer than the night lengths hence the amount of the solar insolation received maximum hence the summer season is experienced with the highest temperatures of the year. The sun is nearer the earth in the months of March and September and furthest from the surface of the earth in the months of June and December. The figure shows the relative distance of the sun in different times of the year; Figure 4: position of the sun in different times of the year In the design of the building, the knowledge on the position of the sun at any location on the surface of the earth is important. This will influence the type of material used in the construction, the ventilation required, the amount of the natural light received and the amount of artificial light acquired. This will ensure that the occupants are comfortable at any time of the year. The cost of acquiring the artificial lighting will also be reduced if proper designing is done which will allow maximum entry of the natural heat. Different techniques can be used to locate the position of the sun on the surface of the earth at different times of the year. The sun’s position on the surface of the earth can be determined by considering the following key component; the sun’s altitude and Azimuth. To calculate these components, knowledge on the latitude, longitude and declination is required. Declination Declination angle is an angle that varies from +23.5 degrees to -23.5 degrees during summer and the winter solstice respectively. It refers to the angular vertical displacement to celestial sphere object from perpendicularly north or south from the celestial equator. It is equal to zero during the spring and autumn equinoxes. Latitude and longitude These components are expressed in degrees; minutes and seconds depending on the precision of the data required and are used to locate any position on the surface of the earth. Equator at 0 degrees is the main latitude in which all the other latitudes make reference to while the main longitude is the prime meridian that runs from the north pole of the earth to the south pole and give the position of a place on the surface of the earth either to the east or west of the prime meridian. Azimuth Is the angle that the sun makes to the true south and can be determined using the sun chart or any other most appropriate method. Altitude Altitude of the sun is the vertical distance of the sun from the earth’s surface. To calculate the altitude of the sun, the following formula can be used. Calculating solar time To calculate the solar time, the following equation can be used; Where; Direct beam intensity To determine the radiation incident on any surface on the building or on the earth’s surface, the equation below can be used; Where; Solar radiation The solar radiation is the earth’s main source of energy, in determining the intensity of extraterrestrial radiation on a plane normal to sun's rays on any day, the formula below is used. Where; ) The solar radiation passes through the atmosphere that contains so many particles, moisture, gases and other small objects that absorb, diffuse, reflect as well as scatter the solar radiation from the sun, therefore the total radiation on the earth’s surface can be obtained as below; To determine the energy received at a particular point on the surface of the earth amount of solar radiation (insolation) received on the that surface has to be calculated, to be able to calculate the insolation some parameters such as the solar declination angle, hour angle and cloud cover of the place and the zenith angle have to be determined. Thereafter, the procedure below is followed. Calculating the hour angle (H); Calculating the Zenith angle (Z); Where; Calculating the solar insolation; Where; Solar loads variation with the diurnal cycle The diurnal cycle takes the whole day which is exactly 24hours, during this period; there are various temperature changes that are experienced due to the position of the sun at different times of the day. Figure 5: solar variation during the day The sun rises in the morning at around 6am, thereafter, the solar loads increase with increase in time to around 12noon when the maximum solar loads are experienced. At this time the sun is directly perpendicular to the surface of the earth. In such a case, considering the temperature change, the maximum temperature is experienced at around 3pm; this is a lag from the time the maximum solar loads are experienced. This occurs because, at this time, the incoming solar radiation is more than the cooling rate by radiation. The solar loads then decrease with time to a minimum at around12am. When the sun sets and the radiative cooling then begin until the minimum solar load is attained at 12am when the temperatures are at the lowest point. Heat transmission through windows Windows have two main functions in a building; they act as the main source of natural light to the building as well as the main ventilation elements of a building. In some cases they also determine the solar energy received in the building, therefore, windows can be modified in different ways so as to minimize the amount of solar radiation received in a building. Different formulas can be used to determine the solar radiation amount received in the building through the windows; in this case, we are going to consider the effect of shading a window on incident radiation by providing simple rectangular overhang over the window. Assume; The figure below shows the above parameters; Figure 6: horizontal overhang on a wall Therefore, the formula for calculating the hourly radiation in the window is given by; Given; Given by; The window-radiation view factor are obtained from standard tables and then used in the given formulae. Conclusion The building materials influence the level of comfort of the occupants. The properties of the materials used such as the transmittance and emissivity determine the amount of heat transmitted through such materials. To achieve the goal of environmentally sustainable buildings therefore, the properties of the building materials must be properly determined. The position of the sun influences to a large extent the amount of heat received in a building, it necessary to determine the position of the sun at different times of the day and also at different times of the year so that the right materials can be selected for building to ensure that the intended occupants receive the comfort they require. From the calculations, it can be seen that the conduction process is the most effective mode when it comes to heat transfer. This therefore means that the process must be controlled to the required level of comfort required. If the buildings are built on the basis of consuming minimum energy, as well as ensuring the comfort of the occupants then the goal on the economy and sustainability of such buildings would be achieved. References Liebmann, B. L., and A. Gruber, 1988: Annual variation of the diurnal cycle of outgoing long-wave radiation. Mon Wea. Rev., 116, 1659–1670. Read More