- Double glazing reduces energy loss by conduction. The gap between the two pieces of glass is filled with a gas or contains a vacuum.
- Particles in a gas are far apart. It is very difficult to transfer energy. There are no particles in a vacuum so it is impossible to transfer energy by conduction.
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Practicle Insulation 2
- Loft insulation reduces energy loss by conduction and convection:
- Warm air in the home rises.
- Energy is transferred through the ceiling by conduction.
- Air in the loft is warmed by the top of the ceiling and is trapped in the loft insulation.
- Both sides of the ceiling are at the same temperature so no energy is transferred.
- Without loft insulation, the warm air in the loft can move by convection and heat the roof tiles.
- Energy is transferred to the outside by conduction.
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Practicle Insulation 3
- Cavity wall insulation reduces energy loss by conduction and convection:
- The air in the foam is a good insuator.
- The air cannot move by convection because it is trapped in the foam.
- Insulation blocks used to build new homes have shiney foil on both sides to reduce energy transfer by radiation.
- Energy from the sun is reflected back to keep the home cool in summer.
- Energy from the home is reflected back to keep the home warm in winter.
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Conduction, Convection and Radiation
- Energy can be transferred by:
- Conduction- due to the transfer of kinetic energy between particles.
- Convection- a gas expands when it is heated. This makes it less dense so it rises. The unit of density is kg/m³ or g/cm³.
- density = mass ÷ volume
- Radiation does not need a material to transfer energy. Energy can be transferred through a vacuum.
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efficiency = useful energy output (x 100%) ÷ total energy input
- Energy transformations can be shown by Sankey diagrams.
- Energy from the source (home) is lost to the sink (environment).
- Different types of insulation cost different amounts and save different amounts of energy.
Payback time = cost of insulation ÷ annual saving
- Everything that transfers energy will waste some of the energy as heat to surroundings.
- Buildings that are energy efficient are well insulated; little energy is lost to surroundings.
- Designers and architects have to make sure that as little energy as possible is wasted.
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