Pollution Free Ecofriendly Solar Powered Air Conditioning System Thermoelectricity can be used for electric power generation (Seebeck effect) or for heating/cooling applications (Peltier effect). Electric power generation has not only been very successful for specialized applications such as satellites, but also to generate electricity at remote places using gas heaters and to make use of wasted-heat sources at low temperature. Cooling applications have only succeeded in low power applications such as camping coolers and small (hotel) refrigerators. For higher thermal power other cooling technologies overcome thermoelectricity by attaining better performance and lower prices. Thermoelectric camping coolers are successful because the lack of fluids and pumps makes TE option the most robust and reliable alternative for portable equipment. Moreover, the cost is low because just one module has enough power and no electronic controls or amplifiers are needed. Hotel refrigerators are small and do not need much cooling power to keep some bottles just a few degrees cooler than the room temperature (usually no freezing temperatures are required). In this case reliability is not critical. Apparently, no thermoelectric air-conditioning solution could succeed in a market dominated by refrigeration cycles, where vaporcompression refrigeration is the most widely sed method for air-conditioning of public places and residences. However, there are situations in which air-conditioning systems are difficult to install while a thermoelectric option may
become worthy. This project presents such a thermoelectric cooler that has been designed to operate on solar power, thereby making it useful for a variety of applications .
Theory We make use of the property that when we apply a voltage to a thermocouple; a temperature difference develops between the two junctions of the thermocouple. This is called the Peltier Effect. The direction of heat transfer is controlled by the polarity of the applied voltage. Thus, in principle, the same device can be used for heating as well as cooling purpose by reversing voltage polarities. Consider the circuit shown in Fig 1. The right-hand junction is heated, showing that electrical energy is being transformed into heat energy, while heat energy is transformed into electrical energy at the left junction, thereby causing it to be cooled. When the current is reversed, these junctions are reversed.
could be used as an air-conditioner in the summer and as a heater in the winter
A combination of the semiconductors Bismuth and Telluride is most commonly used for the thermocouples. The semiconductors are heavily doped, which means that additional impurities are added to either create an excess (Ntype semiconductor), or a lack (P-type semiconductor) of free electrons. Early thermocouples were metallic, but many more recently developed thermoelectric devices are made from alternating p-type and n-type semiconductor elements connected by metallic interconnects. Charge flows through the n-type element, crosses a metallic interconnect, and passes into the p-type element. If a power source is provided, the thermoelectric device may act as a cooler, as shown in Fig 2. Electrons in the n-type element will move opposite the direction of current and holes in the p-type element will move in the direction of current, both removing heat from one side of the device. An interesting consequence of this effect is that the direction of heat transfer is controlled by the polarity of the current; reversing the polarity will change the direction of transfer and thus the sign of the heat absorbed/evolved. Besides, these devices could do more than cool a room on a hot summer day. Because the Peltier effect is reversible, needing only the electric current to flow in the opposite direction, such a device
The proposed air conditioning system is divided into following phases or modules: Phase 1—Development of a refrigeration unit Phase 2--Solar powering the unit Phase 3--Converting the refrigerator into an cooler The first phase implements a refrigerator using a Peltier element. The refrigerator consists of an insulated box with the Peltier element attached to it. A Peltier control circuit is used to convert the AC
mains supply into a 12 volt regulated DC supply. A temperature sensor indicates the temperature inside the refrigerator, which is displayed on a LCD panel. The second phase consists of a solar panel. The solar panel converts the light energy from the sun into electricity and this drives the refrigerator during the day while a battery unit takes over during the night. Alternatively, the refrigerator can also be run on AC power supply during the night if the battery gets discharged. The third phase converts the refrigerator into a cooler. A 12- volt fan was placed at the door of the refrigerator to allow the cold air to be blow out and cool the surrounding area. In the following section, we shall discuss each of these proposed units in detail. PROPOSED MODEL This section gives the detailed description of the different modules used in the project. The different modules are: • Refrigeration unit • Temperature sensor unit • Peltier control unit • Solar unit The Refrigeration unit consists of a Peltier element attached to an insulated aluminum enclosure. The Peltier element is attached to a heat sink to dissipate the heat generated during TE cooling. A switching circuit is also used to change the polarity of the current being given to the Peltier element. This enables the user to use the device for cooling as well as for heating, according to his requirements. A 12 volt fan is also fitted in the enclosure to blow the cool air from inside the enclosure to its immediate surroundings. Moreover an LM35 temperature sensor is placed inside the enclosure to sense the temperature. The Temperature sensor circuit consists of a LM 35 temperature
sensor that is connected to an LCD, after interfacing it with 89S52/Arduino, to display the temperature in the enclosure. The Peltier control circuit is a simple SMPS (Switched Mode Power Supply) circuit that converts the regular ac mains power supply into a regulated 12 volt dc supply required to drive the Peltier element. The solar unit, consists of a photovoltaic cell, a Volume Unit (VU) meter and a 12 volt rechargeable battery to store the energy. The solar cell is connected to the VU meter which is connected to the input to the thermoelectric element. The battery is also connected to the peltier element’s input. Solar cell is a semiconductor device that converts the energy of sunlight into electric energy. These are also called ‘photovoltaic cell’. Solar cells do not use chemical The output (product of electricity and voltage) of a solar cell is temperature dependent. Higher cell temperatures lead to lower output, and hence to lower efficiency. The level of efficiency indicates how much of the radiated quantity of light is converted into useable electrical energy. Solar cell efficiencies vary from 6% for amorphous silicon-based solar cells to 42.8% with multiple-junction research lab cells. Solar cell energy conversion efficiencies for commercially available multicrystalline Si solar cells are around 14-16%. The highest efficiency cells have not always been the most economical — for example a 30% efficient multijunction cell based on exotic materials such as gallium arsenide or indium selenide and produced in low volume might well cost one hundred times as much as an 8% efficient amorphous silicon cell in mass
production, while only delivering about four times the electrical power. SALIENT FEATURES OF THE PROPOSED MODEL Here we discuss the benefits of both these technologies over the other available alternatives. Thermoelectric coolers are solid state heat pumps which have no moving parts and thus are inherently reliable and require little or no maintenance. They are ideal for cooling devices that may be sensitive to mechanical vibration. Thermoelectric devices are also strong in demand for both heating and cooling in the face of a changing operating environment; here a simple switching of thermoelectric current polarity allows the system to shift to the mode required. In addition, unlike compressor technology, thermoelectric system components can be mounted in any physical orientation and still function properly. Of course, one other advantage of thermoelectric systems is that they do not require the use of evaporative chemicals, like CFCs, which may be harmful to the environment. Hence its use is very promising in domestic applications and mainly where installation of conventional equipment is problematic (historic buildings, aesthetic, technical difficulties, size restriction). Thermoelectric devices, therefore, open up a whole new world to cooling and heating possibilities and can be used over a wide range of applications. Originally developed for energy requirement for orbiting earth satellite – Solar Power – have expanded in recent years for our domestic and industrial needs. Solar power is produced by collecting sunlight and converting it into electricity. This is done by using solar
panels, which are large flat panels made up of many individual solar cells. It is most often used in remote locations, although it is becoming more popular in urban areas as well. (a) The major advantage of solar power is that no pollution is created in the process of generating electricity. Environmentally it the most Clean and Green energy. Solar Energy is clean, renewable (unlike gas, oil and coal) and sustainable, helping to protect our environment. (b) It does not pollute our air by releasing carbon dioxide, nitrogen oxide, sulfur dioxide or mercury into the atmosphere like many traditional forms of electrical generation does. Therefore Solar Energy does not contribute to global warming, acid rain or smog. It actively contributes to the decrease of harmful green house gas emissions. (c) Solar energy does not require any fuel. (d) There is no on-going cost for the power it generates – as solar radiation is free everywhere. Once installed, there are no recurring costs. (e) It can be flexibly applied to a variety of stationary or portable applications. Unlike most forms of electrical generation, the panels can be made small enough to fit pocket-size electronic devices, or sufficiently large to charge an automobile battery or supply electricity to entire buildings. (f) It offers much more self-reliance than depending upon a power utility for all electricity. (g) It is quite economical in long run. After the initial investment has been recovered, the energy from the sun is practically free. Solar Energy systems are virtually maintenance free and will last for decades.
(h) Its not affected by the supply and demand of fuel and is therefore not subjected to the ever-increasing price of fossil fuel. (i) By not using any fuel, Solar Energy does not contribute to the cost and problems of the recovery and transportation of fuel or the storage of radioactive waste. (j) More solar panels can easily be added in the future when your family’s needs grow. It does not only reduce your electricity bill, but will also continue to supply your home/ business with electricity in the event of a power failure. (k) A Solar Energy system can operate entirely independently, not requiring a connection to a power or gas grid at all. Systems can therefore be installed in remote locations, making it more practical and cost effective than the supply of utility electricity to a new site. (l) They operate silently, have no moving parts, do not release offensive smells and do not require you to add any fuel. CONCLUSION This project will demonstrates the use of novel and innovative technologies for implementation of an air conditioning system. The air conditioning system is employed using a Peltier element and powered by solar energy. It is felt by the authors that this eco-friendly initiative can be used for local refrigeration and heating applications. The proposed model is implemented using appropriate hardware discussed in the text and the results obtained are satisfactory. It is seen that reasonable cooling can be achieved using our proposed model. Although the prototype works well in small enclosed space, a more versatile
version may be developed for general purpose applications. The temperature variations achieved using our prototype is of the order of 20550 C. The DC power source to the Peltier element is a solar cell panel. The prototype can be modified according to specific requirements by changing the Peltier element by a series-parallel combination (Thermopile Peltier element) to achieve greater degree of temperature variations. Further, the prototype can be made a intelligent system by incorporating signal processing and signal conditioning elements. REFERENCES [1] Muhammad Ali Mazidi and Janice Gillispie Mazidi, “The 8051 Microcontroller and Embedded Systems Using Assembly and C”, 2nd edition, Prentice-Hall, Inc, New York [2] E. Rudometov & V. Rudometov, "PC Overclocking, Optimization and Tuning”, 2nd Edition, Independent Publishers Group, 2002 [3] Muhammad H. Rashid, “Power Electronics: Circuits, Devices, and Applications”, Prentice Hall, Inc., 2003 [4] Christophe P. Basso, “Switch-Mode Power Supplies: SPICE Simulations and Practical Designs”, McGraw Hill, 1st Edition, 2008 [5] S. Maruyama, A. Komiya, H. Takeda, and S. Aiba, “Development of Precise-temperature-controlled Cooling Apparatus for Medical Application by using Peltier Effect”, International Conference on Biomedical Engineering and Informatics, pp. 610-614, May 2008 [6] A. Sokolov, V. Gostilo, A. Loupilov, and V. Zalinkevich, “Performance improvement of Si(Li) Peltier cooled detectors”, 2001 IEEE Nuclear Science
Symposium Conference Record, pp. 176-179, 2001 [7] Mingcong Deng; A. Inoue, and S. Goto, “Operator based Thermal Control of an Aluminum Plate with a Peltier Device”, Second International Conference on Innovative Computing, Information and Control, pp. 319-319, 2007 [8] Qi Yaqing, Li Zhihua, and Zhang Jianzhong, “Peltier Temperature Controlled Box for Test Circuit Board”, 22nd International Conference on Thermoelectrics, pp. 644-647, 2003 [9] S. Aijb, “Profitability of using solar energy for refrigeration and air conditioning”, IEEE INMIC 2001, pp. 30-37, 2001 [10] J. Primozic, and R. Svecko, “Control in Refrigeration Systems”, IEEE ICIT 2003, pp. 1040-1045, 2003 [11] F. Unezaki, Y. Anzai, T. Ikeda, and F. Matsuoka, “Energy Saving Refrigeration System for Supermarket”, Eco Design 2005, pp. 482-483, 2005
