P1- KEEPING HOMES WARM (2)

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CONDUCTION, CONVENCTION 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 for density Kg/m3 or g/cm3.

DENSITY = MASS/ VOLUME

RADIATION - Radiation does not need a material to transfer energy, Energy can be transferred between a vacuum.

B- A*

PRACTICAL INSULATION

Double galzing 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 . There are no particles in a vacuum so it is impossible to transfer energy by conduction.

Loft INSULATION =reduces energy loss by conduction and convection:

energy is transferred through the ceiling by conduction

air in the loft is warmed by the top of the ceiling and is warmed by the loft insulation

both sides of the ceilning are the same temperature so no energy is transferred

without loft insulation warm air can move by convection and heat the roof tiles

energy is transferred by the outside by conduction

warm air in the home rises

CAVITY wall insulation reduces energy loss by conduction and convection:

the air in the foam is a good insulator

the air cannot move by convection because it is trapped in the foam

INSULATION BLOCKS used to build new homes have shiny 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

D-C

ENERGY EFFICIENCY

ENERGY TRANSFORMAIONS can be shown by Sankey diagram

ENERGY from the source (home) is lost to the sink environment.

Different types of insulation cost different amounts and save different amounts of energy

ENERGY EFFICIENCY ( B-A*)

Everything that transfers energy will waste some of the energy as heat to the surroundings

Buildings that are energy efficient are well insulated; little energy is lost to the surroundings

Designers and architect's have to make sure that as little energy as possible is wasted

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