Keeping Homes Warm – Revision Pack (P1)
Conduction, Convection & Radiation:
Conduction happens due to the transfer of kinetic energy between particles.
Convection happens in gases and liquids. When a gas is heated, it expands and takes up more space (more volume) – this means that it is less dense (or less heavy) so it can rise; this can be explained by:
Density = Mass / Volume
If the volume that the gas takes up is more, and the mass is the same, the density will be lower so the gas will be able to rise.
Radiation does not need a material to transfer energy – energy can be transferred through a vacuum (empty space).
Insulation:
Double glazing reduces energy loss by conduction. The gap between the two pieces of glass is filled with a gas or vacuum. Particles in a gas are far apart, and there are no particles in a vacuum so it is not possible to transfer energy via conduction.
Loft insulation reduces energy loss by both conduction and convection:
STEP 1 – warm air in the home rises
STEP 2 – energy is transferred through the ceiling by conduction
STEP 3 – air in the loft is heated by the ceiling, but is trapped by the loft insulation
STEP 4 – both sides of the ceiling are the same temperature so no energy is transferred
STEP 5 – any energy that reaches the roof is transferred to the outside by conduction – loft insulation prevents this from happening
NOTE – if you didn’t have loft insulation, hot air in the loft would move by convection and heat the roof tiles, and then move to the outside by conduction.
Cavity wall insulation works in a similar way to loft insulation – it reduces energy loss by conduction and convection. An insulating material is blown in between the brick outside wall and the inside wall. This stops air from circulating in the cavity (the gap) because it gets trapped in the foam – this prevents energy loss by convection. The air in the foam is a good insulator, so little energy is lost by conduction.
Insulating blocks used in modern houses have a shiny foil on both sides. In the summer, this reflects the energy from the sun to keep the house cool. In the winter, energy from the home is reflected back into the house to keep it warm.
Energy Efficiency:
The equation for energy efficiency is:
Efficiency = Useful energy output (x100%) / total energy input
Energy from the source (home) is lost to the sink (environment).
Different types of insulation cost different amounts of money and save different amounts of energy. The equation for payback time is:
Payback Time = Cost of insulation / Annual Saving
NOTE - Everything that transfers energy will lose some of the energy as heat to the surrounding environment. Energy cannot be destroyed, only transferred.
Buildings that are efficient are well insulated – this means that little energy is lost to the surrounding area.
Those who design houses must make sure that the house is very efficient.
Past Papers:
PPQ(1):
PPQ(2):
PPQ(3):
PPQ(4):
PPQ(5):
Mark Schemes:
PPQ(1):
PPQ(2):
PPQ(3):
PPQ(4):
On next page...
PPQ(5):