Reducing Energy Loss (WJEC GCSE Science (Double Award)): Revision Note

Reducing Energy Loss

• Energy that is dissipated to the surroundings is often the main source of wasted energy transfers

• If these unwanted energy transfers can be prevented, or reduced, the useful energy transfers can be made more efficient

Reducing Conduction

• Energy transfers by heating due to conduction are one of the most common sources of dissipated energy

• To reduce energy transfers by conduction, materials with a low thermal conductivity should be used

  • Materials with low thermal conduction are called insulators

Reducing Convection

• Convection can also be a source of dissipated energy 

• To reduce energy transfers by convection, convection currents must be prevented from forming

• Therefore, the fluid (liquid or gas) that forms the currents must be prevented from moving

Insulation

• Insulation reduces energy transfers from both conduction and convection

• The effectiveness of an insulator is dependent upon:

  • The thermal conductivity of the material

    • The lower the conductivity, the less energy is transferred 

  • The density of the material

    • The more dense the insulator, the more conduction can occur

    • In a denser material, the particles are closer together so they can transfer energy to one another more easily

  • The thickness of the material

    • The thicker the material, the better it will insulate

 Loft Insulation

• Insulating the loft of a house lowers its rate of cooling, meaning less energy is transferred to the surroundings (outside)

  • Insulation is laid between the timber joists in the loft space reducing heat loss by conduction and convection

  • Insulation is reinforced plastic composed of woven material with glass fibres laid across and held together

  • The air trapped between the fibres makes it a good insulator

  • The insulation is often made from fibreglass (or glass fibre)

  • The fibreglass panels often have a foil coating to prevent heat loss by radiation

Cavity Wall insulation

• The gaps or cavities between external walls are often filled with insulation

  • This is called cavity wall insulation

  • This is often done by drilling a hole through the external wall to reach the cavity and filling it with a special type of foam which is made from blown mineral fibre filled with gas

  • This lowers the conduction of heat through the walls from the inside to the outside and reduces convection in the wall space

Cavity Wall Insulation

Less energy is transferred by conduction and convection if the cavity is insulated

Double Glazing

• Windows are an area of significant heat loss in houses

• Double glazing in windows is an efficient way to reduce heat loss

  • Double glazed windows consist of two panes of glass with air trapped between them

  • The trapped air acts as an insulator preventing heat loss by conduction and convection

Comparison of Double and Single Glazed Windows

Double glazing reduces heat loss by conduction through the glass

Draught Proofing

• Draught proofing means stopping any draughts that may be present in the home by sealing, filling or blocking any gaps that may be present

• Draughts can be caused by:

  • Gaps between the skirting boards and the walls

  • Wall vents

  • Plug sockets

  • Gaps in the seals between the windows, window sills and walls

  • Gaps between floorboards

  • Key holes and letter boxes

  • Gaps between doors and the floor

• Draught excluders are often cylindrical tubes of stuffed fabric that block the gap between the door and the floor

  • You can also get tape, brushes or foam that can be fixed on the bottom of a door to perform the same function

• By stopping the draughts between rooms, or between the outside and inside of a door, the convection currents are reduced resulting in less heat loss

Different Types of Draught Excluders

All draught excluders work by blocking the gap between the door and the floor to prevent draughts

Comparing Methods of Reducing Energy Loss

• Each method of reducing energy loss has its advantages and disadvantages

• Aspects to consider are:

  • Initial installation cost

  • Potential savings to energy bills

  • Payback time (the time it will take for the savings made to equal the initial cost)

Comparison of Insulation Types Based on an Average Three Bedroom House

Payback time can be calculated using the following equation: