5 U-values All buildings waste heat Different materials lose heat at different ratesHomes need to be insulated to reduce heat lossU-values compare rate of heat loss through different materials. They measure how quickly heat travels through a material
6 U-values Measured in W /(m2 oC) W-Watts (heat loss) m2-area of materialoC-temperature difference
7 Example calculation 25Wats Area of material 2m2 Temperature difference 20 oCU value = 25 / (2x20)U=0.625 W/(m2 oc)This is a low U value, a good insulator.
8 High and low U-values High value U-values lose heat more quickly Low value U-value lose heat more slowlyMetals have high U-values (good conductors)Insulators have low U-values, (ie foam)
13 Payback time Pay back time = initial cost / annual saving Buying insulation costs moneyBut you could save in the long termOver time the money you save on bills equals the money spent, this is payback time.
14 Payback Time and Energy Efficiency P1b Keeping Homes Warm13/04/2017PPayback Time and Energy EfficiencyCopy and complete the table below:InsulationCostAnnualSavingPaybackTime (Yrs)Loft Insulation£400£80Double Glazing£2,000£50Cavity Wall Insulation£600£60Draught Excluder£40£205yrs40yrs10yrs2yrsDouble GlazingWhich type of insulation costs the most?Which type of insulation is the most effective?Which type is the most “cost effective”?Which type pays for itself after 40 years?Loft InsulationDraught ExcluderDouble GlazingJames Ferguson Claydon High School
15 Payback Time and Energy Efficiency P1b Keeping Homes Warm13/04/2017Payback Time and Energy EfficiencyAn ordinary light bulb is 8% efficient. If it uses 1,000J of electrical energy how much energy is wasted as heat?useful outputenergy=efficiencytotal inputXuseful outputefficiency X total inputuseful outputenergy=0.08 X 1,000useful outputenergy=80Jwaste energy = 1,waste energy = 920JJames Ferguson Claydon High School
16 Payback Time and Energy Efficiency P1b Keeping Homes Warm13/04/2017Payback Time and Energy EfficiencyA gas boiler wastes 260J for every 1,000J of energy it is supplied with. What is the efficiency of this appliance?efficiency =total input energyuseful output energyuseful outputefficiency X total inputefficiency =1,000740efficiency = 0.74efficiency = 0.74 X 100 = 74%How could the waste energy be reduced?Insulate the boiler and hot water tank, lag the pipes and service the boilerJames Ferguson Claydon High School
17 Copy a completeHeat flows from a hotter place to a _________ place. The heat flow is ________ if the material has a lower U-value. Insulating the wall reduces heat losses because it _______ the walls U valueUse these words: cooler, reduces, slower