P1 Revision 3

  • Created by: LBC0502
  • Created on: 14-06-14 12:30
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  • P1 Revision
    • Insulating Our Homes
      • Roof - Convection - Loft insulation
      • Floor - Conduction - Carpets (trap air)
      • Doors - Convection - Draft excluder/physical barrier
      • Windows - Conduction - Double/triple glazing (expensive)
      • Thermal energy is transferred from the water to the air: cold water through boiler - convection. Hot water to radiator - convection, conduction and radiation.
      • Windows - Radiation - Curtains/blinds
      • Between walls, there are convection currents and conduction of thermal energy. Double glazing has a vacuum or trapped air. Vacuum prevents conduction and convection (no particles). E.g. silver foam behind radiator to reflect thermal radiation.
      • Walls - Conduction - Cavity wall insulation, trapped air
    • Heating and Insulating Buildings
      • Experiment: Does double glazing really work? Hot water is poured into a small beaker and another small beaker which is inside a larger beaker and lids are put on both beakers. IV: time. DV: temperature of water inside beaker.
      • House Insulation: wall insulation, windows (glazing- vacuum or trapped air between sheets of glass), floors (carpet), doors (draft excluder), blinds/curtains, loft insulation, cap chimney.
      • Conclusion: The single beaker cooled down at a faster rate. The double beaker cooled down slowly. This is because the double beaker had more trapped air which is the best insulator of thermal energy.
      • Fuel poverty: people spend half (or more) of their income on heating bills.
    • U-Values
      • A material or part of a house with a low U-value is a good insulator.
      • E.g. Windows in a house will transfer energy quickly so the windows will have a higher U-value.
      • The higher the U-value, the more quickly the energy is transferred.
      • 270mm Cavity wall with insulation: 0.6. Double glazed window: 2.9. Roof of material 100mm thick: 0.3. These items have a low U-value. Therefore, they are good insulators of thermal energy.
      • The rate of losing energy for each part of a building depends on the U-value.
    • Solar Panels and Payback Time
      • Solar panels cost £250. Solar panels save you £100 per year. £250/£100 = 2.5 years = 2 years 6 months.
      • In a boiler, hot water would be at the top and cold water would be at the bottom (hot water is less dense and cold water is more dense).
      • Payback Time = Cost to install / Annual Saving
      • Best design for solar panel: large surface area, black matt, solar panel gains thermal energy from infrared radiation and this will heat the water (will emit thermal enegy back into pipes with water flowing in them).
      • Payback Time: Solar panels are expensive to install. Home-owners need to decide whether likely savings made is worth the cost of installing the panels. This calculation is known as the payback time.
      • Two types of solar panels: one uses sunlight to heat water. The other converts sunlight into electricity directly. These are known as photovoltaic cells (e.g. calculators).


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