# P1 Revision Cards

P1 revision cards for keeping homes warm

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• Created by: Eleanor.1
• Created on: 18-04-14 18:48

## Practical Insulation

• 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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• 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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## Energy Efficiency

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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