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Boardworks GCSE Science: Physics Heat Loss and Insulation

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Presentation on theme: "Boardworks GCSE Science: Physics Heat Loss and Insulation"— Presentation transcript:

1 Boardworks GCSE Science: Physics Heat Loss and Insulation

2 Boardworks GCSE Science: Physics Heat Loss and Insulation

3 Boardworks GCSE Science: Physics Heat Loss and Insulation
A temperature problem Boardworks GCSE Science: Physics Heat Loss and Insulation Touch a piece of metal and a piece of wood at the same temperature. Which material feels warmer and why? The metal feels cold and the wood feels warm. Metal is a good conductor and conducts the heat away from your hands, so it feels cold. Teacher notes Student could be asked to try this experiment if the materials are available. Wood is not a good conductor and does not conduct the heat away from your hands as well as the metal, so the wood feels warmer than the metal.

4 What are thermal insulators?
Boardworks GCSE Science: Physics Heat Loss and Insulation Some materials are very poor conductors of heat. These are called thermal insulators. Examples of materials that are insulators include plastics, wood, ceramics and air. Air becomes a very effective insulator when it is trapped and stopped from moving. This is how your clothes keep you warm – air is trapped between the fibres and so acts as an insulator. Other insulating materials, including polystyrene and loft insulation, use trapped air because it is so effective.

5 Charlie the Chef and his frozen chicken!
Boardworks GCSE Science: Physics Heat Loss and Insulation Charlie forgot to take the chicken out of the freezer last night! Will his plan to defrost the chicken in time for lunch work? Teacher notes The illustration could be used to develop students’ understanding of the relationship between heat loss and insulation. Left: It is am and Charlie, our forgetful, rosy-cheeked, woolly-jumper-wearing chef, is staring at a very frozen chicken, which needs to be ready for lunch. What can he do to speed up the defrosting process? Right: Five minutes later in the same kitchen and Charlie has transferred his woolly jumper to the frozen chicken, mistakenly convinced that this will warm up the chicken and help to defrost it! These illustrations can be used to tackle the common misconception that insulation makes an object warm and explain that insulation actually prevents heat transfer between an object and its surroundings, so Charlie’s plan is destined for failure. Students could be given coloured traffic light cards and asked to vote on whether Charlie’s plan will be a success. The activity could be extend by asking students to explain their voting.

6 How does a vacuum flask work?
Boardworks GCSE Science: Physics Heat Loss and Insulation How is a vacuum flask able to keep hot drinks hot and cold drinks cold? 2. The plastic (or cork) lid is an insulator and the screw top prevents convection currents escaping from the flask. 1. There is a vacuum between two layers of glass or steel, which prevents heat leaving or entering by conduction. 3. The walls have silvery surfaces, which prevent heat leaving or entering by radiation.`

7 Boardworks GCSE Science: Physics Heat Loss and Insulation

8 Boardworks GCSE Science: Physics Heat Loss and Insulation
Heat loss from houses Boardworks GCSE Science: Physics Heat Loss and Insulation A thermogram shows the distribution of heat over the surface of a house. It highlights where heat is being lost. The white, yellow and red areas are the warmest, so these are the worst insulated parts of the house. The blue and green areas are the coolest, so these are the best insulated parts of the house. Photo credit: Alfred Pasieka / Science Photo Library Thermogram of a house showing the distribution of heat over its surface. The colour coding ranges from white to yellow for the warmest areas (greatest heat loss) through red to purple and green for the coolest areas (greatest insulation). This thermogram shows that the roof and windows (yellow) are poorly insulated, while the walls (red, purple and green) are losing the least heat. Thermograms are often used to check houses for heat loss, so that they can be made more energy efficient through improved insulation. A poorly insulated house loses more energy and so costs more to heat. It also means that more pollution, particularly carbon dioxide, is created in order to heat the house.

9 Boardworks GCSE Science: Physics Heat Loss and Insulation
Heat loss from houses Boardworks GCSE Science: Physics Heat Loss and Insulation Where is the most heat lost from a poorly insulated house? roof 20% windows 12% Teacher notes It should be stressed that these values are for an average poorly insulated house. walls 36% doors 4% floor 28%

10 How can heat loss be reduced?
Boardworks GCSE Science: Physics Heat Loss and Insulation Various types of insulation can prevent the loss of heat energy from a house. Use the following slides to complete this table showing how different types of insulation can prevent loss of heat energy from a house. Type of insulation Type of heat transfer stopped How insulation stops heat transfer

11 Can heat loss through windows be reduced?
Boardworks GCSE Science: Physics Heat Loss and Insulation A lot of heat energy can be lost through windows. Double glazing adds an extra pane of glass. The air trapped between the two panes acts as an insulator and reduces heat loss by conduction. insulating layer of air side-view of double glazing The insulating effect of the gap can be improved by removing the air and creating a vacuum. Teacher notes This slide could be used to start a discussion about the advantages and disadvantages of double glazing and how it’s use is compulsory when building new houses. Triple glazing could also be discussed. It offers better insulation against heat loss than double glazing, but this saving does not cover the extra cost of installing triple glazing. However, triple glazing offers additional benefits, such as improved noise insulation. The problems with double glazing are that it can be expensive and that it is difficult to break in emergencies without a special hammer.

12 How can heat loss through walls be reduced?
Boardworks GCSE Science: Physics Heat Loss and Insulation Most outside walls have an empty space between the two layers of bricks called a cavity. convection currents in the cavity The air trapped in the cavity acts as an insulator and reduces any heat loss due to conduction through the bricks. Heat loss can also occur due to convection within the cavity. Plastic foam insulation can be pumped into the cavity to prevent this. foam insulation prevents convection currents Teacher notes It should be highlighted to students that older brick and stone buildings do not have cavity walls. It can be expensive to fit cavity wall insulation to old buildings but it is easy to add to new buildings.

13 How can heat loss through a roof be reduced?
Boardworks GCSE Science: Physics Heat Loss and Insulation The air warmed by radiators (and other heaters) is carried around a house by convection currents. heat loss The house becomes heated but, if there is no roof insulation, the warm air continues to rise. The heat eventually escapes through the roof and is lost due to conduction through the roof tiles. loft insulation Loft insulation contains trapped air and so forms an insulating layer between the loft and the rest of the house. This helps to reduce heat loss through the roof.

14 How can heat loss from radiators be reduced?
Boardworks GCSE Science: Physics Heat Loss and Insulation A radiator produces infrared radiation. Some of this heat energy is absorbed by the wall that the radiator is attached to, and so the wall heats up. This can be a real problem on outside walls, where the heat energy absorbed by the wall can escape from the house. Heat loss from a radiator can be reduced by placing shiny foil between the wall and the radiator. The foil prevents heat radiation from reaching the wall by reflecting it back into the room. This method of insulation is very cheap to install.

15 How can heat loss through doors be reduced?
Boardworks GCSE Science: Physics Heat Loss and Insulation A draught is the movement of air due to a convection current. A lot of heat energy can be lost from a house due to draughts escaping through gaps under doors and around windows. This is one of the easiest types of heat loss to prevent. Draught excluders are hairy or spongy strips that can be used to close the gaps around doors and windows. They prevent draughts escaping and so reduce heat loss.

16 How can curtains reduce heat loss?
Boardworks GCSE Science: Physics Heat Loss and Insulation A draught is the movement of air due to a convection current. Warm air rises and is carried up towards the windows in a house by convection currents. This heat energy can escape through gaps around windows that are uncovered. Fitting curtains and closing them can prevent draughts leaving a house and so reduce heat loss. In addition, curtains are opaque and so radiated heat does not pass through them.

17 How does insulation affect heat loss?
Boardworks GCSE Science: Physics Heat Loss and Insulation Teacher notes This activity could be used to show the effect of insulation on the fuel bill for a poorly insulated house. Changes to the insulation can be made individually or in combination, allowing students to investigate the effect of several simple insulation methods.

18 Insulation and heat loss – true or false?
Boardworks GCSE Science: Physics Heat Loss and Insulation Teacher notes This true-or-false activity could be used as a plenary or revision exercise on insulation and heat loss. It could also be used at the start of the lesson to gauge students’ existing knowledge of this subject matter. Coloured traffic light cards (red=false, yellow=don’t know, green=true) could be used to make this a whole-class exercise.

19 How does double glazing work?
Boardworks GCSE Science: Physics Heat Loss and Insulation How does double glazing keep a house warmer? Double glazing keeps a house warmer because there is a layer of a__ between the panes of glass. ir Air is a poor c________, so it acts as an i_______. onductor nsulator The trapped air r_______ heat loss by c_________ from a house. educes onduction side-view of double glazing

20 Insulation and heat transfer
Boardworks GCSE Science: Physics Heat Loss and Insulation Teacher notes This classification activity provides the opportunity for some informal assessment. Coloured traffic light cards (green=conduction, yellow=convection, red=radiation) could be used with this activity to increase class participation.

21 Boardworks GCSE Science: Physics Heat Loss and Insulation

22 Boardworks GCSE Science: Physics Heat Loss and Insulation
What is payback time? Boardworks GCSE Science: Physics Heat Loss and Insulation Payback time is the time it takes for the cost of installing insulation to be equalled by the savings made from reduced energy costs. payback time (in years) = cost of insulation saving each year Example: Adding silver reflectors behind radiators costs £25 and saves £50 per year. Teacher notes It should be highlighted that the payback time is measured in years and that the shorter the payback time, the quicker fuel bill savings will pay for the cost of installing the insulation. payback time = 25 50 = 0.5 years (6 months)

23 Calculating payback time
Boardworks GCSE Science: Physics Heat Loss and Insulation What is the payback time for these types of insulation? How heat escapes Cost of heat escaping per year Cost of insulation Payback time roof windows draughts walls £80 £40 £50 £100 £240 £3,200 £50 £500 3 years 80 years 1 year 5 years Why is double glazing popular if the payback time is so long?

24 Which insulation is most cost-effective?
Boardworks GCSE Science: Physics Heat Loss and Insulation Cost-effectiveness is a comparison of the annual savings in reduced energy bills and the cost of insulation. Cost-effectiveness = saving each year cost of insulation Example 1: Example 2: Adding silver reflectors behind radiators costs £25 and saves £50 per year. Adding draught excluders costs £50 and saves £50 per year. Teacher notes Calculating cost effectiveness is an alternative to calculating payback times and allows different types of insulation methods to be compared. It should be made clear that insulation types with larger cost-effectiveness factor values are more cost-effective than insulation types with smaller values. Cost-effectiveness = 50/25 Cost-effectiveness = 50/50 = 2 = 1 So, the reflectors are more cost-effective than the draught excluders.

25 Calculating cost-effectiveness
Boardworks GCSE Science: Physics Heat Loss and Insulation Teacher notes This ordering activity could be used as a plenary or revision exercise. Mini-whiteboards could be used to make this a whole-class exercise.

26 Boardworks GCSE Science: Physics Heat Loss and Insulation

27 Boardworks GCSE Science: Physics Heat Loss and Insulation
Glossary (1/2) Boardworks GCSE Science: Physics Heat Loss and Insulation cavity wall – A wall made up of two layers of bricks with an air gap between them, which reduces heat lost by conduction. cavity wall insulation – Plastic foam insulation that is pumped into the gap in a cavity wall to prevent heat lost due to convection in the cavity. cost-effectiveness – A comparison of the annual savings in reduced energy bills and the cost of insulation. double glazing – Two panes of glass with an air gap between them, which reduces heat lost by conduction. The air can be sucked out of the gap to create a vacuum. draught excluder – A hairy or spongy strip that prevents draughts escaping through the gaps around doors and windows, and so reduces heat loss.

28 Boardworks GCSE Science: Physics Heat Loss and Insulation
Glossary (2/2) Boardworks GCSE Science: Physics Heat Loss and Insulation loft insulation – A material which contains trapped air and helps to reduce heat lost through the roof of a house. insulator – A material that is a very poor conductor of heat and so can be used to reduce heat loss. payback time – The time it takes for the cost of insulation to be equalled by the savings from reduced energy bills. vacuum flask – A vacuum flask is a bottle with double walls separated by a vacuum. It reduces heat transfer and so keeps warm drinks warm and cold drinks cold.

29 Boardworks GCSE Science: Physics Heat Loss and Insulation
Anagrams Boardworks GCSE Science: Physics Heat Loss and Insulation

30 Boardworks GCSE Science: Physics Heat Loss and Insulation
Multiple-choice quiz Boardworks GCSE Science: Physics Heat Loss and Insulation Teacher notes This multiple-choice quiz could be used to assess students understanding of heat loss and insulation. The questions can be skipped through without answering by clicking “next”. Students could be asked to complete the questions in their books and the activity could be concluded by the completion on the IWB.


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