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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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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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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