Keeping homes warm

Question 1

How does double glazing reduce energy loss by conduction?

Answer 1

• 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.

Question 2

How do loft insulations reduce energy loss by conduction and convection?

Answer 2

• 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.

Question 3

How does cavity wall insulation reduce energy loss by conduction and convection?

Answer 3

• The air in the foam is a good insulator.
• The air cannot move by convection because it is trapped in the foam.

Question 4

How does the shiny foil on both sides insulation blocks reduce energy transfer by radiation?

Answer 4

• 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.

Question 5

Energy can be transferred by:

Answer 5

• Conduction - due to transfer of kinetic between particles.
• Convection - a gas expands when it is heated. This makes it less dense so it rises.
• Radiation does not need a material to transfer energy. Energy can be transferred through a vacuum.

Question 6

Unit for Density.

Answer 6

Kg/m³

Question 7

Density

Answer 7

Question 8

Efficiency formula

Answer 8

Question 11

Sankey diagrams and energy transfer

Answer 11

• Energy transformations can be shown by Sankey diagrams.
• Energy from the source (home) is lost to the sink (environment).
• 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 architects have to make sure that as little energy as possible is wasted.