Natural Sciences Grade 7 Term 3 Energy and

Natural Sciences Grade 7 Term 3: Energy and Change Insulation and energy saving

Topic 4 Insulation and energy saving Using insulating materials [part 1] Natural Sciences - Grade 7

Using insulating materials Materials that are heat insulators: • keep cold items cold; • slow down heat transfer from the surroundings; • keep hot items hot; • slow down heat transfer from the hot item to the cooler surroundings; • insulated window coverings [awnings; curtains; blinds; etc. ]. • In summer it is closed [minimize heat gain] to cool the house and block out the sun’s radiation. • In winter it is kept open to allow the sunlight through the house. Natural Sciences - Grade 7

Types of insulators • Materials that contain air spaces, are the best insulators. • Examples: - thatched roof [air is trapped in the spaces between the grass of the thatch] - wool - cork - straw - feathers - grass - styrofoam Natural Sciences - Grade 7

Insulators are used to reduce heat transfer Styrofoam • It is made from polystyrene [a type of plastic; plastic is a poor conductor of heat]. • It is also used to make food packaging [picnics; take-away meals; hot coffee; etc. ]. • The food in styrofoam boxes can be kept warm / hot. Natural Sciences - Grade 7

Insulators are used to reduce heat transfer Ceiling insulation • It minimizes heat gain during summer. • It minimizes loss of heat during winter. • It is mostly made from fibreglass strands [air is a poor heat conductor and it becomes trapped between the fibreglass’ strands ; the amount of heat loss/gain is limited; stops conduction and convection from taking place]. • Foam can be sprayed in the roof structure above the ceilings. • Blanket insulation can be rolled out above the ceilings. Natural Sciences - Grade 7

Insulators are used to reduce heat transfer Materials that keep us warm • Woollen clothing prevents the body heat from escaping, e. g. jerseys; woollen hats; gloves; jackets; etc. • Bedding, e. g. blankets; duvets; comforters; etc. • It keeps people warm when it is cold. The air is trapped between the fibres and therefore extra insulation is given. • Thermal jackets worn by Russian, Eskimo and Norwegian people keep them warm in temperatures that are below 0°C. Natural Sciences - Grade 7

Insulators are used to reduce heat transfer Insulating vacuum flasks and cool boxes • Insulating materials such as plastic and styrofoam are used to make cooler boxes [foam / sponge materials are excellent insulators. They have many air bubbles in the foam. Air is an excellent insulator. • Liquids are kept hot or cold in vacuum flasks. Between the flask and the casing is a vacuum, meaning no air particles. Natural Sciences - Grade 7

Insulators are used to reduce heat transfer Water pipes - Cover water pipes with an insulating material to: Ø prevent water from freezing and water pipes from bursting as well as preventing water waste. Ø prevent loss of heat through the metal pipes and reduce electricity waste. - Water pipes are made from plastic materials [PVC]. Doors Ø Fill the gaps of fitted doors with foam rubber [weather strips] to prevent warm air from escaping. Walls Ø Build outer walls with a double layer of bricks [cavity walls - air space reduces heat transfer]. . Natural Sciences - Grade 7

Insulators are used to reduce heat transfer Traditional / Indigenous homes Ø Roofs and some walls are made of grass which is a good natural insulator. Ø The framework is smeared with mud. Ø Floors are made from cow dung [dries and form a hard, waterproof floor and it is heat insulating]. Ø Rondavels are build with thatched grass roofs [Xhosa]; beehive huts [Zulu]. Natural Sciences - Grade 7