3 of 30 Touch a piece of metal and a piece of wood at the same temperature. Which material feels warmer and why? A temperature problem The metal feels cold and the wood feels warm. wood feels warmer than the metal. Metal is a good conductor and conducts the heat away from your hands, so it feels cold. Wood is not a good conductor and does not conduct the heat away from your hands as well as the metal, so the
8 of 30 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. Heat loss from houses 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. The blue and green areas are the coolest, so these are the best insulated parts of the house.
22 of 30 Example: Adding silver reflectors behind radiators costs £25 and saves £50 per year. Payback time is the time it takes for the cost of installing insulation to be equalled by the savings made from reduced energy costs. = 0.5 years (6 months) What is payback time? payback time (in years) = cost of insulation saving each year payback time = 25 50
27 of 30 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. Glossary (1/2)