Unit 3 - Test topic.pdf

3.1 Energy Conservation LIGHT EMITTING DIODE (LED) Light Emitting Diodes (LEDs) are the most widely used semiconductor diodes among all the different types of semiconductor diodes available today. Light emitting diodes emit either visible light or invisible infrared light when forward biased. The...

3.1 Energy Conservation LIGHT EMITTING DIODE (LED) Light Emitting Diodes (LEDs) are the most widely used semiconductor diodes among all the different types of semiconductor diodes available today. Light emitting diodes emit either visible light or invisible infrared light when forward biased. The LEDs which emit invisible infrared light are used for remote controls. Working: LEDs (Light Emitting Diodes) are semiconductor light sources that combine a P-type semiconductor (larger hole concentration) with an N-type semiconductor (larger electron concentration). Applying a sufficient forward voltage will cause the electrons and holes to recombine at the P-N junction. During this process energy in the form of light is released because electrons make transition from conduction band (high energy level) to valence band (low energy level). Compared with conventional light sources that first convert electrical energy into heat, and then into light, LEDs (Light Emitting Diodes) convert electrical energy directly into light, delivering efficient light generation with little-wasted electricity. Applications of Light Emitting Diodes There are many applications of the LED and some of them are explained below.  LED is used as a bulb in the home and in the industries The light emitting diodes are used in the motorcycles and cars These are used in the mobile phones to display the message At the traffic light signals LED’s are used COMPACT FLUORESCENT LAMPS Everyone knows that one of the biggest advantages of a CFL is its low energy consumption. It also produces less heat, has a much higher life than incandescent or halogen lamps and produces pleasant light. Replacing incandescent lamps with CFLs results in cost savings in terms of electricity bills, that together with its long life offset the higher purchase price of the lamp. How does a CFL bulb save energy? The answer to this question lies in the technology. What is a CFL? Fluorescent lamps and CFLs are very similar. In fact, a CFL is just a compact version of a fluorescent lamp that is smaller and easier to install. The glass tube is bent and both its ends are fixed onto a base that holds the ballast and can fit into standard incandescent bulb sockets. Therefore, there is no major difference between the working principle of a fluorescent lamp and a CFL. Light without heat: Traditionally, light is generated by heating something, whether it is a lighted candle or an incandescent lamp, something has to be heated to the point where it emits light. In an incandescent lamp, electricity is passed through a filament, which is usually made of tungsten. This in turn heats it to a point where it glows and produces light. To prevent the filament from burning, the whole setup is in a sealed vacuum bulb. In incandescent lamps most of the energy is converted to heat and the light produced is just a byproduct of the whole process. It is not surprising then that only about 10 to 12% of the electrical energy consumed is converted to light and the rest is just wasted as heat. In physical terms, an incandescent or halogen lamp is very poor when it comes to lighting efficiency. In fluorescent lamps, light is generated using a very different method without the need to heat anything. It consists of a sealed tube with a coating of fluorescent material on the insides and an electrode at each end. The tube contains mercury vapor. When a voltage is applied across the electrodes, the gas inside the tube gets ionized, conducts electricity and in the process generates ultraviolet (UV) light. When the UV light hits the phosphor coating on the inside of the tube, the material glows to produce visible light. When the lamp is switched on, a component called the ballast produces a high voltage between the electrodes, which is necessary for the initial ionization of the gas in the tube. Once the lamp starts operating, the current and light output can be maintained using a much lower voltage. Unlike incandescent lamps, the little heat produced in a fluorescent lamp is just a byproduct and most of the energy is converted into light. Due to their much better efficiency in converting electricity to light, which is about 40 to 50%, a CFL that produces the same amount of light as an incandescent lamp consumes two-thirds less power and produces very less heat in comparison. GREEN BUILDING A green building, also known as a sustainable building, is a structure that is designed, built, renovated, operated, or reused in an ecological and resource-efficient manner. Green buildings are designed to meet certain objectives such as protecting occupant health; improving employee productivity; using energy, water, and other resources more efficiently; and reducing the overall impact to the environment. Salient features of a Green Building are: Building envelope design Building system design (HVAC, lighting, electrical, and water heating) Integration of renewable energy sources to generate energy on-site Efficient use of water, water recycling and waste management Selection of ecologically sustainable materials (with high recycled content, rapidly renewable resources with low emission potential) Use of energy efficient and eco-friendly equipment Indoor environmental quality (maintain indoor thermal & visual comfort and air quality) Effective control and building management systems BENEFITS OF GREEN BUILDINGS A Green Home can have tremendous benefits, both tangible and intangible. The immediate and most tangible benefit is in the reduction in water and operating energy costs right from day one, during the entire life cycle of the building. Tangible benefits: Green buildings consume 40% ~ 60% lesser electricity as compared to conventional buildings. Green buildings consume 40% ~ 80% lesser water as compared to conventional buildings, by utilizing ultra-low fixtures, rain water harvesting, waste water recycling etc. Green buildings generate lesser waste by employing waste management strategies on-site. Intangible benefits: Enhanced air quality. Excellent day lighting. Health & well-being of the occupants. Conservation of scarce national resources. Enhanced marketability for the project. WASTE WATER MANAGEMENT Nature has an amazing ability to cope with small amounts of water wastes and pollution, but it would be overwhelmed if we didn't treat the billions of gallons of wastewater and sewage produced every day before releasing it back to the environment. Treatment plants reduce pollutants in wastewater to a level nature can handle. Wastewater is used water. It includes substances such as human waste, food scraps, oils, soaps and chemicals. In homes, this includes water from sinks, showers, bathtubs, toilets, washing machines and dishwashers. Businesses and industries also contribute their share of used water that must be cleaned. Wastewater also includes storm runoff. Although some people assume that the rain that runs down the street during a storm is fairly clean, it isn't. Harmful substances that wash off roads, parking lots, and rooftops can harm our rivers and lakes. Effects of wastewater pollutants If wastewater is not properly treated, then the environment and human health can be negatively impacted. These impacts can include harm to fish and wildlife populations, oxygen depletion, beach closures and other restrictions on recreational water use, restrictions on fish and shellfish harvesting and contamination of drinking water. Environment Canada provides some examples of pollutants that can be found in wastewater and the potentially harmful effects these substances can have on ecosystems and human health: Decaying organic matter and debris can use up the dissolved oxygen in a lake so fish and other aquatic biota cannot survive; Excessive nutrients, such as phosphorus and nitrogen (including ammonia), can cause eutrophication, or over-fertilization of receiving waters, which can be toxic to aquatic organisms, promote excessive plant growth, reduce available oxygen, harm spawning grounds, alter habitat and lead to a decline in certain species; Chlorine compounds and inorganic chloramines can be toxic to aquatic invertebrates, algae and fish; Bacteria, viruses and disease-causing pathogens can pollute beaches and contaminate shellfish populations, leading to restrictions on human recreation, drinking water consumption and shellfish consumption; Metals, such as mercury, lead, cadmium, chromium and arsenic can have acute and chronic toxic effects on species. Other substances such as some pharmaceutical and personal care products, primarily entering the environment in wastewater effluents, may also pose threats to human health, aquatic life and wildlife. Wastewater treatment The major aim of wastewater treatment is to remove as much of the suspended solids as possible before the remaining water, called effluent, is discharged back to the environment. As solid material decays, it uses up oxygen, which is needed by the plants and animals living in the water. "Primary treatment" removes about 60 % of suspended solids from wastewater. This treatment also involves aerating (stirring up) the wastewater, to put oxygen back in. Secondary treatment removes more than 90 % of suspended solids. Why Treat Wastewater? It's a matter of caring for our environment and for our own health. There are a lot of good reasons why keeping our water clean are an important priority: Fisheries Clean water is critical to plants and animals that live in water. This is important to the fishing industry, sport fishing enthusiasts, and future generations. Wildlife Habitats Our rivers and ocean waters teem with life that depends on shoreline, beaches and marshes. They are critical habitats for hundreds of species of fish and other aquatic life. Migratory water birds use the areas for resting and feeding. Health Concerns  If it is not properly cleaned, water can carry disease. Since we live, work and play so close to water, harmful bacteria have to be removed to make water safe. BIOGAS PLANT Biogas refers to gases that are derived from the composition of organic materials such as manure and plant remains. These gases can be used as fuels and also to produce electricity. The main composition of biogas is methane. Biogas possesses chemical energy, and therefore electricity from biogas comes as a result of converting this chemical energy to mechanical energy and finally into electricity. This is done by the use of transducers such as generators and turbines that convert energy from one form to another. This electricity can be used both domestically and commercially since it can be made in small and large scale. WORKING Connect the biogas source to the inlet of the gas engine. The biogas source may be a cylinder that contains pressurized gas or directly from a digester, which is the means of decomposing the organic material. The gas engine is designed to work in a similar manner to that of a car, since it is composed of pistons within which the gas is burnt and used to rotate a shaft, converting the chemical energy in the biogas into mechanical energy through motion. Connect the gas engine to the AC generator in such a way that the rotating shaft powers the AC generator. The motion transferred to the AC generator produces electricity through magnetism. Connect the AC generator to cables that transfer electricity to a chargeable battery for storage or directly to a power distribution grid for consumption. Step up the electricity with a transformer to reduce the power lost as electricity is being transmitted through the cables. SOLAR CELL Solar cell is a key device that converts the light energy into the electrical energy in photovoltaic energy conversion. In most cases, semiconductor is used for solar cell material. The energy conversion consists of absorption of light (photon) energy producing electron–hole pairs in a semiconductor and charge carrier separation. A p–n junction is used for charge carrier separation in most cases. Solar cells are semi-conductor devices which use sunlight to produce electricity. They are manufactured and processed in a similar fashion as computer memory chips. Solar cells are primarily made up of silicon which absorbs the photons emitted by sun’s rays. The process was discovered as early as 1839. Silicon wafers are doped and the electrical contacts are put in place to connect each solar cell to another. The resulting silicon disks are given an anti-reflective coating. This coating protects sunlight loss. The solar cells are then encapsulated and placed in an aluminum frame. Working When light radiation falls on a P-N junction diode photons collide with valence electrons and impart them sufficient energy to leave the parent atom. Thus electron-hole pairs are generated in both sides of the junction. These electron and holes reach the depletion layer and are then separated by the strong barrier field existing there. However the charge carrier electrons from the P-side slide down the barrier potential to reach the N-side and the holes in the N-side move to the P-side. Their flow constitutes a minority current that is directly proportional to the illumination and also depends on the surface area exposed to light. SOLAR WATER HEATERS A solar water heater is a device that can be used to capture sunlight in order to heat the water in your pipes to be used for baths, showers, etc. It consists mainly of: a thermal panel (solar collector) installed on the roof; a tank to store hot water; Accessories, such as a circulating pump to carry the solar energy from the collector to the tank, and a thermal regulator. However, a back-up heating system is required for times when there is insufficient luminosity. Working The solar water heater absorbs light by means of a collector placed on the roof and converts it into heat. It passes this heat to a water tank by means of a circulating pump. This exchange is triggered by the thermal regulator, but only when the collector is hotter than the water in the tank. This prevents the circulating pumps using electricity needlessly. Conversely, it also prevents overheating. When there is insufficient sunlight, the water is preheated and a back-up system takes over to bring the water to the required temperature. This system can therefore be used to produce hot water at a constant temperature throughout the year without emitting any CO2.