Construction resources Essay

Construction resources make use of physics in many of their products. Two that I have picked are solar collectors and their use of insutation. Insulators have the purpose of preventing conduction, convection and radiation to unwanted areas. There are a wide range of techniques and materials used in doing this and I am going to look in depth at this idea. The company uses solar collectors in many different ways, their main purpose is to collect solar energy and heat energy. They can be used to heat and power many different appliances. Photovoltaic cells: Photovoltaic cells transfer the energy carried by the electromagnetic waves that make up sunlight directly to an electrical circuit in order to make a current flow. Light excites electrons to move from one layer to another through semi conductive silicon materials. Only a fraction of a volt is produced so a large array is needed to produce appreciable currents, usually about 20W to 100W. The Photovoltaic cells produce DC current so if alternate current AC is desired then an inverter is required. AC form is commonly available from the mains. Solar cells: Sunlight may also be used to heat water directly. This can be done in two ways, water can be circulated through pipes which run through the back of the solar cells, producing water at around 60oC suitable for household use. The other method is to focus sunlight from a large are to a small spot using an array of mirrors, this can produce temperatures of up to 4000oC and it’s quite feasible to produce power stations from this, however it has not been implemented yet. Here is on way in which the hot water can be used, this is quite economical and environmentally friendly. Solar panels are quite versatile and can be put on many roofs of simply in the garden, which makes them popular when it comes to heating swimming pools of hot water for showers. Any material that is a poor conductor of heat and electricity can be used as an insulator. Thermal insulating materials reduce the flow of heat between hot and cold regions. Thermal insulation may have to fulfill one or more of three functions: to reduce thermal conduction in the material, in which heat is transferred by electrons; to reduce thermal convection currents, which can be set up in air- or liquid-filled spaces; and to reduce radiation heat transfer, in which thermal energy is transported by electromagnetic waves. These are three ways in which heat energy can be transferred. Conduction, where heat energy is transferred through solid materials, metals are normally the best conductors. There are a number of factors that affect thermal conductivity. Increasing the area of the cross-section of the solid through which hear flows increases the rate of flow, however increasing the thickness of the wall decreases the flow of heat. Provided that a steady state has been reached (where the temperature of any point is not changing through time) then the rate of flow of heat ? Q/? t is given by: ?Q/? t –> A ? T/? x Besides the physical dimensions of the materials, another factor affecting rate of flow is the properties of the material, the Thermal Conductivity of the materials ? through which the heat energy is travelling is the constant of proportionality in this relationship, so:?Q/? t = -? A ? T/? x The units for thermal conductivity are watts per metre per kelvin. The Quantity ? Q/? t is called the temperature gradient. On my visit to Construction resources I noticed that they have used these Physical conclusions in there insulation. One in particular is ‘Homatherm’ a wall and roof insulator. The slabs are thick which means less flow of heat, and have a thermal conductivity is only 0. 04 W/mK. Conduction in terms of particles: The particles in metals and non-metals are arranged differently, which gives them their different characteristics. In a non-metal the particles have forces between them that can be described like springs. When heat is delivered to the solid the oscillations of the particles being heated will increase in amplitude. For heat to be conducted the neighboring particles must also receive the extra energy, as particles oscillations increase in frequency the neighboring particles also gradually increase in frequency as heat is transferred to them. This is a very slow process. In a metal the arrangement is different, metallic boding occurs between metal atoms where a ‘sea of delocalized’ electrons hold the positive metal ions together in a lattice. It is these free electrons that are responsible for the high conductivity character of metals. When a metal is heated the metals ions vibrate with an increase frequency. When an electron hits these ions with extra energy, they receive this extra energy and move faster. This electron can then travel to another parts of the lattice, to an ion that hasn’t received any of this heat energy and collide with it, transferring its energy to this ion. Now that ion has extra energy and vibrates with a greater frequency. This process is a lot faster as there are many electrons in a metal lattice. U-Values: Architects and heating engineers use U-Values to calculate the flow of heat energy through building materials. The U-Values is quoted for a given thickness of a particular material, and is based on actual measurements made using the material. The U-Value is defined as: U-value = Rate of energy flow Area X Temperature difference Construction resources uses this knowledge of U-Values when designing building materials to reduce the energy wasted in the form of heat going out of the build and to achieve the ultimate goal of reducing CO2 emissions. But there are obvious limitations with reducing thermal conductivity, you can only reduce it to a certain amount, 0. 025 in air, so there will always be heat loss. Also too much insulation in the house will lead to what construction resources refers to as internal pollution. This has lead to construction resources researching in trying to lower the energy that is used to build and transport he construction materials. Bibliography: Microsoft Encarta Heinemann Advanced Science Salter’s Horner’s AS Advanced Physics Strengths and Limitations of Photovoltaic cells: Since one photovoltaic cell only produces a small fraction of a volt, large arrays are required to produce appreciable voltages. This requires a lot of space and the cells need to be in a place where no shadows will be cast on them. This limits what they can be used for. Also the amount of power produced by the photovoltaic cells directly depends on the amount of sunlight, so they cannot be relied on to produce power for something that constantly needs it. The only way this can be overcome is if some power was stored for a rainy day. But this again would take up space. Also an array of solar collector will be expensive and have a long ‘pay back’ time. However it is environmentally friendly and after the pay back time, savings can be made. Also photovoltaic cells can be made look attractive depending on where they are placed. Strengths and Limitations of solar cells: The solar cells have similar limitations to the photovoltaic cells in regards to positioning and cost but a small array is only required to produce enough hot water for something like residential showers or central heating. This is economical and environmentally friendly and solar cells are quite versatile.